Meritous Setup Guide and Walkthrough

Introduction

This is a little short (haha, nothing I write is short) guide to setting up Meritous on a modern system and playing it in a comfortable manner that will then pivot into a sort of mini-walkthrough of the game.

Meritous is an old quasi-roguelike/bullet-hell/shooter hybrid game released in the early 2000s for Windows. It's a simple little SDL game written in C with no bells and whistles or quality of life features in which your goal is to explore a randomly generated 3000 room dungeon, find three artifacts, fight three bosses, and then defeat a final boss in an epic showdown.

Despite being from the Windows XP era, it runs surprisingly well on modern systems, requiring some accessibility tools to be playable to its fullest but otherwise functioning perfectly. That's where this guide comes in.

This is an extremely detailed and verbose document. If you want to just get into the steps to victory, skip down to Putting All This Together. If you just want my notes on Archipelago multiworld stuff, start at Archipelago Multiworld Setup and Notes. These two sections get more detailed, spoilery, and handholding as they go. Stop when you have the info you want.

Getting Meritous

Meritous itself is available from the rather retro looking developer's website. Version 1.2 never had a binary built but the only thing v1.2 did was fix a Linux-specific bug. As a first pass you should be able to grab v1.1, unzip it to a directory, and run meritous.exe to play. Now we can start dealing with some of the anachronisms of the game.

Making Meritous Playable

First, the game's locked to 640x480 resolution and that's bad on a 1080p display and worse on something UHD.

There's a few options for dealing with this. One is to reduce your desktop resolution, but that's silly. Another is to use Windows Magnifier to try to zoom in on the game, but that robs you of screen real estate too. DxWnd probably won't work since it's an SDL game. The more circuitous option I use (since I'm a streamer anyway) is to use OBS to do a Window Capture on Meritous, then right click that source in OBS and break out a resizable view of the game with "Windowed Preview (Source)". You will be able to resize this second copy freely.

Next, Meritous only takes keyboard input. I'm not a fan, especially with how much moving and shooting you have to do. I get around this with JoyToKey. My setup sets the D-Pad and both analog sticks on a 8bitdo gamepad to send arrow key-presses, one face button to space, another to enter, start to P and select to tab. That should give you all of Meritous's controls on a gamepad. Easy.

Phew. That's a bit more work than most just to get a game working comfortably, but we're done with that. On to the fun stuff.

General Controls and Combat

Meritous is an extremely simple game. You go from room to room, looking for stuff and fighting enemies. By default it's keyboard-only but hopefully you can snag JoyToKey if you want to use a gamepad.

There's about a dozen types of enemies that all perform some permutation of "Come at you and shoot bullets, lasers, and stars". You fight them by charging your PSI Circuit and then releasing it to hit them with a psychic attack. When charging, two indicators appear on each enemy: a circle means your attack will hit them and an X means the attack will kill.

For the most part you should only deal in attacks that get the "will kill" indicator. Playing around with plinking enemies down doesn't work very well and may not work at all on certain enemies.

Everything else is automatic. You unlock locked doors by touching them with the right key in your inventory. Artifacts are passives. You pick things on the floor up by touching them.

Dungeon Elements

The dungeon is 3,000 rooms. Fortunately unless you're going for the 100% True End you won't need to enter about 2,000 of these. Each room has a random shape, exits, monster contents, and special tiles. Each special tile can be interacted with either by just standing on it, or standing on it and pressing enter.

In addition to tiles, rooms are filled with enemies. Enemies come in about a dozen flavors but are largely responded to based on two things: how nasty their shot pattern is and if they have multiple forms.

Weak enemies just shoot a single bullet, later enemies can fire wheels of lasers will filling the room with danmaku patterns. More dangerous enemies should be dealt with quickly, of course. Some enemies though have multiple forms. When you kill one, they'll respawn as a weaker version of them self. There's a couple enemies with two forms, and one with either three or four depending on how late in the game you are. Killing these requires careful use of your PSI Circuit because going into deep cooldown just to have the enemy remain is... to say the least... unfortunate.

Enemies scale in power as you get further from the center of the world. To help eyeball this, the color palette of the dungeon changes as you move away. First a sort of deep blue, then a cyan, then darker to lighter grey, and finally gold at the very far reaches of the dungeon. In addition, if you enter a room with a lot of enemies, the palette will shift toward red.

There are a number of challenge rooms in the dungeon too. When you enter these, the palette will shift all the way red and enemies will begin spawning at an alarming rate. The doors will also lock. Defeating all the enemies will give you bonus chests that contain artifacts, stat levels, and PSI Crystals.

Finally there's three types of "special" rooms. These can be scouted out on the map based on their shape:

Stats

You have three key stats leveled via shop tiles in the dungeon and a fourth stat that's important to keep track of.

Reflect Shield is a pretty high priority for grabbing when you can. Circuit Charge and Circuit Refill should be leveled up equally or perhaps even biased toward Refill because having a high Charge and low Refill can put you in cooldown for far too long.

However, in practice each stat should be leveled close to in lockstep with each other because a second source of levels is reward chests from special challenge rooms. Getting these for an under-leveled stat is a waste. If you're aiming for optimal build you can delay opening these until endgame where each free level has the most impact, but it's not necessary and would make the game harder in general.

Your fourth stat is health: the three hearts in the top right of the screen. Each time you take a hit with no shields up, you lose one. When you lose all three you die. Most medium to large foes give one or two hearts when you defeat them so in most cases health isn't a concern unless you go way too deep for your levels and just die.

You cannot increase health with the exception of getting the Agate Knife for 100%ing the map.

Artifacts

There's eight main artifacts, each one providing a significant change to how your character functions. These are found in reward chests in challenge rooms as well.

You'll come across all eight just in the course of finding challenge rooms and such, but the order you get them in can make the middle portion of the game easier or harder. Once you get one, it's always on.

Keys and Progression

Your goal is to find the three PSI Keys. These are in special PSI Key shrines that are visible on the Complete Map as square rooms with square white daises in the middle. Once you enter one, you'll have a challenge room like experience with a ton of monsters that you must defeat to get the key. Then, the key itself may be "tainted by shadow" if your monster completion rate is too low.

These numbers seem high but you're likely to get this just in the course of getting artifacts and finding the PSI Key shrines. Bosses also contribute a pretty big chunk of your counter. Once you have one, you must then find the right boss room for it. Boss rooms are locked with doors that bear a symbol for the correct PSI Key. Once you open a locked door, that door will start the boss once entered. You fight the three bosses in order: Meridian, Ataraxia, and Merodach.

All three boss rooms have the same shape on the Complete Map: a big slightly off-square room with four white pixels in the corners representing the statues in the room.

All three bosses behave roughly the same way: they have three or four phases, a health bar per phase, and bounce around the room while firing a ludicrous number of projectiles at you. Once you defeat them, you leave the PSI Key in their room and that portion of the final run-up is complete.

Each time you defeat a boss, all enemies in the game get stronger. This can increase their PSI Crystal reward but not enough to suddenly make 100%ing your stats possible. It's not really worth worrying about from a PSI Crystal routing standpoint. Do it when it's comfortable for you, or wait until the very end.

With all three bosses defeated, the PSI Seal will spawn somewhere in the dungeon. Typically the furthest room from spawn. The PSI Seal requires 75% monster completion to pick up and, once you do, any remaining monsters in the dungeon will turn into a superpowered form and flock to you. You must escape back to spawn, with the teleport tiles disabled.

At spawn, you fight the final boss who, frankly, if you can defeat Merodach, you can defeat it.

There is an alternate 100% ending that is gained by, at any point before picking up the PSI Seal, getting 100% map completion. Upon entering the final room for 100%, you will gain the Agate Knife. The Agate Knife turns you into a super-powered version of yourself and unlocks the True End and the True Final Boss.

Detailed Source Diving and Dungeon Generation

The dungeon is randomly generated each time you play. The algorithm for doing so is pretty basic. Every dungeon will be exactly 3,000 rooms with the spawn room in the dead center and generation branches out from there until it generates dead ends, using a standard "BSP"/binary-tree approach.

That's not important. What is important is how it decides to place dungeon features. It's all done by room number, but to really use this info you need to know what order rooms are generated in, and you can't really know that. However to give you an idea of room/tile saturation, here's the rules it uses:

Teleports follow a different logic. Namely once all the rooms are generated the generator divides the entire game world into a grid of 8x8 blocks and for each block drops the Teleport on a random tile. If the randomly picked tile is in a special room or otherwise invalid it tries again. If it fails 20 times in a row it gives up on that tile. Failing 20 times in a row is pretty uncommon so you should be able to count on 64 Teleports equally-ish distributed around the dungeon.

PSI Key shrines and boss rooms alternate every 500 rooms. In practice this means most of the time the shrines and bosses fan out from spawn in three different directions. Most of the time. One tidbit you can glean from this is the third boss room will be the last room generated. That means it's more likely than the others to be at a dead end or possibly a far corner.

Your PSI Seal will generate at the furthest room from spawn, on the binary tree, unless that room is a special room already then the 2nd furthest. In rare instances you can get the PSI Seal in a random room in the middle of a corner because the furthest room is a special room. I've had this happen rarely. The most likely scenario here is if the furthest room is your third boss.

As far as difficulty goes, the dungeon is divided into tiers based on logical distance from spawn...

Each tier introduces new enemies to the enemy pool. All enemies, even older ones, have an equal chance to spawn for each enemy generated.

Additionally these tiers are used to pick Challenge Rooms. One Challenge Room will be spawned per tier, in the largest room in each tier. Each Challenge Room will have difficulty appropriate for its tier. This can help order these rooms in order of difficulty and help you pinpoint them more easily.

You can kind of sort of determine major tier transitions by the game music, but the game code delays changing music for a room or two depending on which way you're heading, so you can't change music repeatedly by walking back and forth across the same room transition. However the music transitions should occur around the lines between tiers 1 and 2, 4 and 5, and 7 and 8.

Palette is another story. Assuming you're in a room with no enemies and no special features, your palette is a smooth gradient from blue to grey to gold determined solely by how far from spawn you are. There's no real obvious breakpoint on when you change tiers that I can see; the code that picks palettes is kind of a giant blob of math and I haven't reversed it entirely yet.

Putting All This Together

Starting Out

So you started the game. You are in the spawn room. What do? You can just start wandering at random and letting the game happen. This is the intended experience. If you want a little more guidance though, here we are.

Your first priority is to get a shield level, maybe a few. Without any shield level, any hit takes a heart, and those are hard to recover right now. Wander into a few adjacent rooms and get a feel for your PSI Circuit. Charge it until enemies have a circle and an X around them and you're guaranteed to defeat them. Pick up their PSI Crystals.

Once you have enough, go back and buy some levels. Aim to keep your levels equalized more or less. Scaling is rough in this game.

When you're comfortable with combat, go forth and look for a compass tile and follow its grey needle to, hopefully, the easiest challenge room. If you start encountering enemies you can't handle, go back to spawn and try moving in a different direction to find a compass that points to a different challenge room.

Scouting Challenge Rooms

You'll want to do Challenge Rooms in tier order as noted in Detailed Source Diving and Dungeon Generation. You can shuffle the order a little but diving straight out to tier 5 and doing its room will see you rendered a pair of smoking boots. Start close to spawn in your search for a room.

Once you find it, you may want to scout around for a teleport tile to mark down a checkpoint, and then go back to spawn and spend any PSI Crystals you can. Remember the reward for challenge rooms can sometimes be stat levels, so you want as much bang for your buck as you can get.

Once you enter the room, the chaos begins. Enemies spawn at a pretty set pattern. You will need to carefully minimize your PSI Charge usage so you can fire again quickly. If bullets are getting too thick, feel free to use PSI Charge to clear them even if not everything will be defeated by it. It takes a bit of practice to get the feel for when you should or shouldn't charge. The first room should just be the easiest enemies, so if you get something unexpected try a different room.

Once finished you should get at least one artifact, hopefully some PSI Crystals and stat levels too. Repeat this process with the next room you can find, remembering to go back or find shop tiles to buy stat levels once in awhile.

Once you get the Complete Map, you can gravitate toward PSI Key shrines in your explorations. You need 15%, 40%, and 60% on the monster counter respectively to pick them up but that should come from just normal exploration. PSI Key shrines are like challenge rooms in a way; very full of enemies. Less chaotic though.

Something to keep in mind with both PSI Key shrines and challenge rooms is enemies will not be allowed to walk into them while you're fighting. They'll just wait outside the doors and once the room opens post-battle, they'll flood in. So in some cases you can get a second challenge room style fight right after the first. A bit of a bother but not terrible if you're ready for it.

Hunting Bosses

Unless you're trying to manipulate PSI Crystals and stat levels, you should save the actual bosses for last. Killing them makes every enemy in the dungeon stronger (but can also increase crystal rewards, but not by enough to matter). If you're short of the monster count to pick up a PSI Key, killing a boss gives about 5% and can put you over. Feel free in that case.

If you get stuck on picking up a PSI Key late in the game, use this opportunity to begin scouting for where the PSI Seal will spawn. It will be the furthest room from spawn, logistically. So it'll be one of about the furthest 10 rooms in each corner of the dungeon. Explore out to these corners and try to find the closest teleport tile to them. If you enter the gold palette area and the music becomes this upbeat hopeful heroic theme, you're in a candidate for the PSI Seal spawn.

Once you have about 65-70% monster completion depending on boss count, all eight artifacts from challenge rooms, all three keys, and as many levels as you can get from those explorations, go hunt down the boss rooms. Having all three keys first obviates the problem of having the right key for the right door; you can open all of them.

All the bosses have the same behavior: you have a big room with four statues in it and the boss is a giant shadowy thing that fires omnidirectional bullets and has multiple phases. Each phase typically adds in order: lasers, white stars, white light spears, and black stars that fire shrapnel when they hit a wall. You should keep a statue between you and the boss as best you can, keeping an eye out for shrapnel stars bouncing onto you from behind you.

As long as line of sight is broken, standard bullets and light spears are not dangerous. White stars will tear your shield in half if they hit. Black stars fire so many fragments they'll cut right through your shield too. Focus on avoiding these. When the boss moves into a position where you are threatened in your hiding spot, release a PSI Charge that can clear your side of the room and run to another statue. In the middle, spam charges of a strength you feel comfortable using.

If you run quickly, with the Metabolism Booster, and follow your PSI Charge as you release it, you'll pretty much be immune to everything as the charge deletes bullets and shrapnel stars and the lasers won't do enough to your shield to pierce it. The worst thing you can do is get pincered into a corner by the larger bosses Ataraxia and Merodach. If you have to run through the boss, expect to take some damage.

Once you beat a boss you leave its PSI Key behind, but that's fine there's no use for it any more. Once all three are down, you're ready for the endgame.

If you get walled and just need more levels to push through, your best option is to run all the way out to a far corner of the map you haven't explored yet, where the palette turns gold and near there, and hunt the small circle enemies that fire lasers and black stars. These give far, far more PSI Crystals than anything in the game short of the escape sequence enemies.

Endgame

Now a decision: Do you want to go for 100%? If yes, you need to go enter every single room in the dungeon, not picking up the PSI Seal if you find it. When you enter the last room, the Agate Knife will appear. The Agate Knife maxes your stat levels, doubles your health, and puts you onto the True End track.

If you're going to do this, ignore PSI Crystals. Only release your PSI Charge if you have to to avoid taking health damage. Run like a bat out of hell from room to room. You have everything in the dungeon, there's no need to stop for anything. If you want to grab levels on the way, wait for a crystal collector tile to pick them up. If you're at about 1,000 rooms at this point expect this to take 3-5 hours depending on how fast you are.

Once you're ready, 100% or not, teleport to the far corners of the map (hopefully you found tiles out there when you were exploring). You need to find the "furthest room from spawn", but this is by room connection logic, not as the crow flies. So it may not necessarily be the far corner. It will be in a zone with a gold palette and the candidate list should be pretty short. If you enter a room and there's a glowing white circle on the floor you found it. Pick it up. Now the escape begins.

Teleport tiles are disabled; you must walk back to spawn in the dead center of the map. To make it harder, the physical features of spawn (the walls and shop tiles) are removed. You have to identify spawn by its location and general shape. Also if you didn't 100% the enemies, super-powered monsters will appear and chase you. These monsters either have a ton of forms or are immortal but will also give you an absolute ton of PSI Crystals if you want them for some reason.

When you reach spawn, the final boss fight begins. Truthfully, if you can take Merodach, this should be easier. The statues are replaced with giant stone blocks that block even more shots and the strats from prior bosses still work. This boss only has two phases, too. Unless...

If you have the Agate Knife the boss begins a third phase (flashing warning here, holy crap). This phase is calibrated to need the agate knife. The entire screen will fill with bullets, the boss will move faster than you can run. Your best bet is to try to get the boss stuck on the blocks where half its shots are invalidated before they're even visible. If you can do that, unload medium PSI Charges into it. If it breaks loose and you're threatened, fire small ones. If it gets up in your space and you need to move, fire a medium one and follow it to the other block.

People say this fight is mostly luck. With the Agate Knife I didn't find it bad, but YMMV.

Depending on a two phase or three phase boss you'll get a different ending. Also if you played on "Wuss Mode" you'll be denied the final story and given a fairly insulting ending screen. Meh. Still an accomplishment in my eyes.

Archipelago Multiworld Setup and Notes

Setup

First you need Meritous Gaiden aka meritous-ap. This is a fork of Meritous that adds AP support, local itemizer, and makes some changes outlined in the appropriate section below.

Any assistive technology used for Meritous will be needed for Meritous Gaiden.

Next you'll need to set up meritous-ap.json in the same directory as the EXE for AP support. The format is as follows:

{
    "ap-enable": true,
    "server": "ws://archipelago.gg",
    "port": 56063,
    "password": null,
    "slotname": "Zap"
}

If this file exists and ap-enable is true, Meritous Gaiden will connect to AP on launch, and keep trying. If you're doing local itemizer rename it or set ap-enable to false.

For generating your AP yaml file, you can use the official generator but a better tool is the unofficial one as it has more complete settings and better UX for forbidding specific check locations and such.

The most major difference when playing Meritous Gaiden is your shop tiles for Shield, Circuit Charge, and Circuit Refill are replaced with Alpha, Beta, and Gamma caches. These are check shops. Each time you buy from one, you get a check. Each category has its cost tracked individually and has 25 checks in it. This totals 75 checks and represents most of the checks you get in a Meritous seed.

25-30 additional checks come from chests in challenge rooms, PSI Key shrines, boss fights, and the world items: the Cursed Seal and the Agate Knife. The two world items are always vanilla by default given their massive game-ending nature.

In addition, one new artifact has been added: The Portable Compass. This item, when C is held, activates the compass overlay. Neat toy!

The item pool consists of...

Gaiden introduces a bunch of unnecessary flashing visual effects. Shields past about level 12 now flash, and a bug has been introduced to the map that causes the entire map to flash if you scroll to a location that has no visible teleport tile in some situations. You can stop the map flashing by scrolling to a location where a teleporter is visible again; can't do much about the shield.

Gaiden also changes the story in really shallow ways but does not change the core gameplay loop, balancing, etc. So if you're playing randomizers you probably just ignore the story bits anyway. What few there are. It also changes "Wuss mode" to "Training mode" and removed the insulting ending screen for it.

The pause button now opens a massive menu of interesting data points including your time to down each boss, death count, crystal pickup count, etc.

Aside from these changes, everything else should be the same. No new QoL features, rebalancing, or other tweaks.

Settings and Ensuring A Smooth Seed

If you just use the default settings for your yaml file, you might end up with a rough time. To quickly break down options and my thoughts on them:

Game Difficulty

This isn't an AP setting. It's picking normal or training mode at the start. The differences boil down to mostly boss difficulty. I wall hard on the third boss on normal mode without some good check luck. Normal/Training does not matter for AP purposes. An ending is an ending.

Training mode might also reduce the cost of Cache Checks, which will be discussed under Item Cache Cost Scaling below, but for now suffice to say this is a good thing. I need to find out for sure.

Goal

There's three options

The only real choice here is Any Ending, or maybe Seal if for some reason you can't beat the normal ending boss or could get thrown into true ending unexpectedly.

Cursed Seal is "Do everything but the final boss, even walking into the final boss room". True Ending is "100% the entire 3000 room map". True End is likely 2-3x the run length versus Any Ending and is far beyond the scope of a one-off multiworld.

Include PSI Keys

This decides if the three mandatory progression items are distributed to the item pool or are in vanilla locations. It's kind of defeating the point of multiworld to put them in vanilla because this renders the entire seed beatable as vanilla, with no support from other players (at least if you're god-tier at the game and can do it with only levels/artifacts in your world).

If on, the three PSI Key shrines will give random checks, so struggling to get to them might not be worth it. PSI Key check volume for effort is really bad versus challenge rooms and early caches.

Include Evolution Traps

Defaults to off. In vanilla every boss kill increases the difficulty of the monsters across the dungeon. In AP, this is simulated with Evolution Trap checks that are forced into boss slots. If randomized, they are whammy checks that could be anywhere and killing a boss grants a normal check instead.

You run the risk of someone finding one early and screwing you if randomized, but if not randomized there is no reason to defeat bosses except to begin the endgame. Matter of preference. I take the risk because having the bosses produce checks adds some sense of direction to a multiworld seed.

Item Cache Cost Scaling

This is a big one. You have three options that set the cost of item caches to 100%, 75%, and 60% of normal respectively. Cache scaling goes bonkers in the final third of the curve and on Normal/100% you can consider the last few checks just outright unreachable. You can reduce this here and also running in Training Mode might reduce it further (todo: find out).

I don't think there's shame in dropping this to the most reduced option of 60% if you're aiming for a one-sitting seed. On normal anything past Cache 20 or so will be faster to just complete the seed to get. However by default, the settings forbid progression items from being in the top 6 caches of each type, so factor that in your decision too.

I need to do more science here to give more firm details.

Pretty standard AP option. If anyone with the DeathLink tag dies, everyone does. Matter of preference. In normal difficulty you have limited lives and no good control over when you can save; probably best to not. In training mode you have infinite lives and it could be amusing.

Item Accessibility and Progression Balancing

These are global flags to try to control where in the seed AP puts your own progression items. They're kind of weird Meritous because you only need the three PSI Keys to beat the seed, but some of the more useful artifacts are flagged as progression items too.

I haven't messed with Item Accessibility much.

You might want to slide Progression Balancing down if you find your early checks are flooding people with progression and access items. This will bias progression items to appear later in the pool. If you do this you might want to exclude late caches if you're frequently done with the seed before you open them. It's a weird balanacing game around the vibe of your group.

Item Selector

This is the real power feature of AP that isn't exposed in the standard tools, but you can manually edit any yaml file to utilize it; or use the unofficial tool.

Every item that can be a check is in a list, and can be dragged to one of four columns. The columns impact logic like so:

The Start Inventory Mode is not relevant for Meritous as there's not enough of any item to overflow max quantity.

If you check a box next to an item, you start with a free hint for where that item is.

Some thoughts for customizing an experience:

Location Selector

Power feature number two! Same UI as Item Selector except check locations instead of items; three columns:

Checking the boxes here start you with a hint for what is in that location.

Thoughts for this...

Note: As far as progression items go, only the PSI Keys and some artifacts count. Everything else, even having enough Shield levels to survive a battle, is non-progression and can be put anywhere. So even if you carefully curate your experience with priority and exclude locations, you might get walled by shoddy level/artifact drop luck. To quote a friend: "That's rando, baby!"

Playing in a Multiworld

This presumes you've beaten the vanilla game, or at least have read my vanilla give above. If something doesn't make sense, look there.

First Minutes

You are, in essence, an early check generator. You have 100-110 checks available and a great number of them will come early in the seed. Your Item Caches will have their first 10 levels fly by then slow before they grind to a halt, and your challenge rooms will generate another 25 checks as you explore and follow the compass. After that, your check sources will be one-offs in PSI Key rooms and, if you didn't leave Evolution Traps vanilla, boss fights.

Due to the disjoint in checks out vs checks in early in the seed, you will likely be forced into BK Mode (slang: blocked, might as well go to Burger King) or to delve into places too hard for your Shield and Circuit levels. If your Circuit level is too low to one-shot enemies in an area you should probably avoid it.

The PSI Crystal reward checks you or others find cap out at 2000 PSI Crystals. After about 20 minutes into the seed they'll be useless as your Item Cache costs inflate to hundreds of thousands (or millions!) of crystals.

Your early goal should be getting the first 3 to 5 levels of each Item Cache by running around spawn and gathering Crystals. At the same time if you find some compass tiles, try to figure out where the easiest challenge rooms are. Challenge rooms will always be a grey needle on the compass.

Once it's no longer feasible to just farm Crystals for Item Cache levels, start hunting for challenge rooms. Any time you find a teleport tile, check if you can buy a new Item Cache check and warp to spawn to do it if so. Remember if you can afford an Item Cache, one of your three stat levels will flash in the HUD. This is because the Item Caches share level shop tile logic from vanilla.

You should pretty much bee-line to any challenge room you can find on the compass, stopping only if you enter an area too hard to proceed. Challenge rooms are the second best source of checks, behind Item Caches you'll be gathering Crystals for anyway. This open exploration should continue until you run out of challenge rooms.

Your ability to proceed out to harder challenge rooms or move into mid-game is largely determined by your levels, and whether or not you have combat artifacts like Shield and Circuit Booster.

Any time you're stuck, prioritize exploring for challenge rooms, then exploring out to the corners, then just farming PSI Crystals.

Mid-game

Next step: by hook or crook, find the PSI Key shrines and loot those. Depending on your group and seed settings, you might opt to skip these entirely unless someone hints for an item and it's in one. These also keep the vanilla rule of "You must have enough monster kills to loot them"

In this mid-game section you should be fairly responsive to hints from your group. Hints in PSI Key shrines are just a matter of you going to pick them up if you have the monster completion. You should have all the Reward Cache checks from doing challenge rooms already. Item Cache hints can be flexed toward a tiny bit if they're close but if something pops in Item Cache 25, you might want to just focus on ending your seed and releasing.

You're beholden to someone finding your PSI Keys to continue from here. If you're BKed, trying to go far afield to farm Crystals from hard foes might nudge things forward a bit. You can also use your BK time to start exploring out to the four corners of the map with the mission of finding the furthest afield teleport tiles you can and taking out foes to raise your monster completion rate. This will be important for the endgame.

Once you have a PSI Key, you should be pointed toward that boss's room by the compass. Boss fights are the same as vanilla, and will yield an Evolution Trap, or a normal check if you randomized those. These should likely be left for last or when you're bottomed out on checks. They either make the world harder with Evolution, or give you one normal check for a lot of legwork otherwise. If the former, there's almost zero reason to do them until you're ready to end.

Bosses and End-game

Once you're confident you can make a smooth transition to endgame and have your PSI Keys, time to start hunting bosses.

At this point, your goal is to end the seed and you can do it in about 15 minutes if you don't divert. Doing other people's checks is probably slower over all. "Endgame" basically means "Okay I can do the bosses, I'm gonna end the seed and stop doing checks for people"

If you randomized Evolution Traps each boss gives a check, and that may inform when you start doing these. Otherwise put them off until the end indeed!

Everything here follows the vanilla guide: take the three PSI Keys to the three boss rooms, defeat the bosses, go to the furthest room from spawn to get the PSI Seal, then do the escape and final boss. The main difference is your levels and artifacts may be vastly different: superior or inferior to vanilla. You have to be ready to fight a boss with fewer levels than you want.

If you opted to set the goal to be "Return the seal", you don't even need to kill the final boss!

One thing that might change is if you're not playing a "Release on completion" game. You might need those really expensive Item Caches. There's one good way to get that many PSI Crystals: the super enemies that spawn when you pick up the PSI Seal. They seem to be invincible and drop PSI Crystals every time you phase them. They drop a ton, but it's still going to take some work.

If you get a PSI Key in Item Cache 25, I actually don't know what you're supposed to do (: