This will work backwards, going from Trial IV to I, as that's the progression I followed in solving these myself. From that experience, I would say the difficulty of the secrets also follows that line, for the most part: IV is the first one that really clues you in on the fact that there's some deeper puzzle, III's solution comes a bit easier, then II and I are pretty tough. Before getting into each trial individually, here's a few very minor hints that might help:

• There is nothing hidden inside any of the main boss rooms (the ones with the red runes that expand) before, during, or after the fight.
  
• None of the secrets depend on your performance in the boss fights—except, of course, you surviving them.
  
• None of the secrets require you to abstain from taking pickups.
  
• The secrets in trials II, III, and IV are not character-specific in any way.
  
• Each trial's solution is separate from one another. There are no repeat gimmicks, with the exception of one part of I and II's solutions.
  
• Some dialogue from NPCs are hints. Which ones those are will be pointed out later on.

With that said, the following sections will be focused on the individual puzzles and be divided into steps. Not every step is a puzzle on its own per se, but each step has some important thing you do or discovery you make, hinted at more and more though minor and major hints, with the takeaway or solution, as well as the explanation, listed at the end.

This will likely be the first trial you go through where you realize there's some wider puzzle at play, not just the simple one-room puzzles in Trial III which give you health and damage.


Minor hint: Take a look at this room—the ghost's dialogue is a subtle nudge:

Minor hint: Notice how the symbol displayed in the center is symmetrical.

Major hint: The way the room is laid out makes it look as though there should be a tunnel doing through the breakable blocks, no?

Solution: The ghost's dialogue (I believe) is meant to give you the impression that what you do needs to be exact and meticulous. The symbol in the center resembles the room you're in, but rotated, with a triangle shape in the center. All of this points to the final arrangement—you need to break the blocks such that it matches the empty space on the other side of the room, thus creating a figure in the center and an outline underneath that are both symmetrical. I've outlined the blocks you need to break in green and the empty space you reference from in red. You'll know you get it right when the broken device lights up. The console dialogue I believe is simply lore, possibly referring to the player characters.



Minor hint: Take a look at the room right after the Lucid Dream fight with the scattered blocks.

Minor hint: The ghost's dialogue is a big hint.

Major hint: Look at the bottom-left section of the blocks... does that shape look familiar?

Major hint: Try doing the trial again up to this point, then looking at this room again. Keep in mind the ghost's dialogue.

Takeaway: The ghost's dialogue is meant to indicate that this room changes. You might notice that the block layout changes from run to run. If you solved the symmetry puzzle previously on that same run, then the blocks on the bottom-left section will match the blocks that you broke in that room. Indeed, the scattered blocks in this room are divided into four sections, and each section corresponds to one of the rooms with breakable blocks, and will match whichever blocks that you broke. This is why the room changes.


Minor hint: Take a look at the first room.

Major hint: Now that you know how the changing room works, there's one final connection to make. What arrangement might you want to make with the blocks?

Solution: You need to make it so that the blocks in the special room match up with the symbol shown to you at the start. To do this, take note of which blocks you break as you go through the breakable-block rooms, then match that up with the four quadrants of blocks at the end. Breaking the right blocks should be easy from there, but if you still want help, here's the block arrangements you'll need in the other three rooms:





Once this is done, the blocks inside the changing room will now be breakable and have the key waiting for you!

Minor hint: The answer has something to do with the pushable blocks.

Minor hint: It also has something to do with the fact that you can push the blocks off of goal tiles, even after the puzzle is solved.

Major hint: Take a look at this room:


Solution: After opening the door, push the block into the exit.


Major hint: Notice that the block is now in the next puzzle room. What can you do with now?

Solution: Keep pushing it into the exit, of course! Any pushable block moves an even number of spaces (even if it hits a wall), but that block is offset from the others by one tile, so you can move it into spaces you can't with the other blocks—namely, the exits to all of the other puzzle rooms. So, keep repeating this step until you hit something new.


Major hint: You might be stuck at the new puzzle. Try to plan out where you want to push the block to, then, before shooting, make sure that the row and column the ship is at does not have line of sight to a laser block. There's no time limit to this, so go slow and be extra careful!

Solution: If you still need the help, here's illustrated instructions courtesy of Wooph's trial answer guide: https://images.steamusercontent.com/ugc/53583854471575335/EE9A58DE143FF65D5AA112A2ECA71270823CB01E/


Minor hint: Once you're past the hard puzzle, you can't push the block into the exit any further.

Major hint: See any other conspicuous places to push the block into?

Solution: Into the center! Then you're done!

Minor hint: When you go through this trial normally, one NPC's dialogue is notably different from the rest, aside from the one talking about the terminal.

Minor hint: Take a look at this room:

Pay close attention to the ghost's dialogue.

Major hint: "Take a moment to pause and catch your breath." The text scrolling even stops briefly before and after "pause" for emphasis.

Major hint: You can see there's a hole in the tiling on the pause menu. Knowing this, remember the other things the ghost told you.

Solution: Go to the spot where there's a hole in the pause menu, then stand still. After a few seconds, you'll see red particles appear, then after a few more seconds, a black ghost, which from this point on I will call a "shadow", appears. The dialogue isn't significant, but the takeaway is: rooms can have holes in the pause menu, where there is a shadow which appears if you remain still at that spot for a little bit.


Minor hint: The shadow you discover in step 1 is not the only one.

Major hint: Take a look at this room:


Solution: Between the first and second heat bars are some breakable blocks, letting you access a nook where the pause menu hole is. There is another shadow at this spot.


Minor hint: Take a look at this room:


Minor hint: Recall what the second shadow told you: "Trapped. | We are trapped. | There can be no freedom without sacrifice."

Major hint: The toggling blocks deal damage if they solidify on top of you. This is important.

Solution: The shadow's line "We are trapped" refers to the ghost blocks. Most would likely think to try breaking all of the ghost blocks, some even before discovering the shadows, but would get to this room and think you can't. But you can break the block, by taking Quickening at the terminal, then killing yourself on the toggling blocks to break it with the death lasers.


Minor hint: Take a look at this room:


Major hint: Since the circle is so easy to avoid here, chances are high you haven't actually seen what happens when you touch it.

Solution: Touch the circle. Exploding ghosts will spawn, but they'll destroy the blocks in the corners of the room in doing so, allowing you to break the ghost block.


Major hint: At this point you've likely broken all ghost blocks and are wondering what to do now (if you haven't then do that). What would the one who mentioned them being trapped have to say now that they are free?

Solution: Go to the end of the trial where the second shadow was, and try to get it to appear. The key will appear instead.

Minor hint: Take a look at this room:


Minor hint: The solution has nothing to do with the miniboss.

Major hint: This step here is the main reason I arranged the trials backwards in this guide. You'll need knowledge from one of the other trial's puzzles here. How could something be hidden inside this empty room?

Solution: If you look at the pause menu, you'll see yet another hole. Sure enough, a shadow will appear there if you remain still at that spot.


Minor hint: Notice anything new inside the following room?

Major hint: That flame is the "cold light" that the shadow was referring to.

Solution: Use a bomb to extinguish the blue flame inside the walls. Also, this isn't required to get the key so I'll say this here: rooms from this point on will periodically have shadows giving you pieces of a story, to check each room for holes, including this one.


Major hint: That first blue flame was not the only one.

Solution: There are two more blue flames you need to extinguish, and because of their placement, you need to make sure you don't use bombs anywhere else so you have them to use on the flames. The last of the three is slightly more hidden, but I'm sure you can find it!


Minor hint: You might have gotten to the end of the trial and to the robot NPC that only says ". . ." after following the previous steps, confused as to why nothing's different at the end. Well, if you got to that point, you missed something earlier.

Major hint: Take a good look at the room which changes in a notable way after extinguishing the flames.

Solution: Inside the last room with pickups, the one that gets almost completely darkened if by this point the music is basically gone, there is now another exit on the right side, hidden by the blackened tiles around it.


Major hint: Having trouble navigating the rooms? Shooting the walls will reveal tiles. And as a general dodging rule, it's good to double back as ghosts are spawning to bait them away from where you're trying to go, as to not get boxed in or stuck for too long on blocks you can't see.

Solution: Thanks to steam user Atlas, we have a full map of the chase sequence, which should help tremendously if you still need help with that. Once you reach the room with the key, you know you are safe.


Once all that's done, you should have all 4 keys, and finally be able to take on Trial V! Good luck: it is one hell of a challenge, and stands head and shoulders above the other four trials.