These are what we call the 'YMMV items.' Things that some people find in this work. We call them 'your mileage might vary' because not everyone sees these things in the same way. This starts discussions in the trope lists, a thing we don't want. Please use the discussion page if you'd like to discuss any of these items.
YMMV: The Floor is Jelly
Crowning Moment of Funny: With the 100% Completion reward unlocked, it's possible to experiment with the SET command in the terminals located in houses so that inputting certain values ensures that the ground does not stop jigglingnote A good example of doing this is setting the DECAY, POWER and TRANSFER values to .98, .025 and .75 retrospectively. If you do this in the opening or sunrise area, birds will fly out of trees when the ground they're rooted to starts bouncing like usual but since the ground will now keep jiggling instead of gradually calming down, they endlessly fly around all confused like!
The Disc One Final Dungeon lacks the life and flora that gave life to the previous areas, and features three sections in which you jump from platform to platform in low gravity to find a key to the portal in the central area, and then backtrack through the section back to the central area, which is made harder on the way back with the addition of glitch blocks which have the same effect on your character as the game's regular Spikes Of Doom. In addition, 6 of the game's 31 secret houses required for 100% Completion are gradually Lost Forever in this area as you obtain these three keys since the hidden entrances to the rooms they're found in are permanently blocked off by said glitch blocks.
The Very Definitely Final Dungeon features various glitchy jelly physics not encountered in the game's other areas, with some rooms practically requiring sheer luck with these glitchy physics to get through. While The Floor is Jelly itself was a well received game, most reviewers bashed this last level for this reason. In fact, if you find the game's very last secret area after the jelly physics have frozen but before the very last screen, you'll find what appears to be an apology from the developer written in platforms.
I'm so sorry for this level it is a cruel and terrible shenanigan...
The Disc One Final Dungeon can be pretty unnerving for some, mainly the lifeless nature of the stage but especiallywhen the game starts glitching up as you make progress, especially when the glitch tendrils starts coming for you after leaving the stage and drags you into the real final stage.
The Very Definitely Final Dungeon itself is no better, with the strange pink background glitching up occasionally and the fish swimming about in erratic glitchy patterns, not to mention the different glitchy jelly physics which at one point the platforms practically collapse beneath your feet. Oh, and for the grand finale, the jelly physics stop completely, resulting in the platforms becoming fully solid, and then a few screens later massive glitching emerges from the edges of the screen and swallows up everything, before everything returns to normal for the ending scene.
The "Speedrun" achievement requires you to beat the game within an extremely tight 30 minutes. For comparison, the current fastest speedrun beat the game in over 22 minutes. You'll practically need to memorise the puzzle solutions in the Wetlands stage, the erratic placement of the deadly glitch blocks in the Disc One Final Dungeon, and have tons of luck with the glitchy physics in The Very Definitely Final Dungeon.
The "Minimalist" achievement requires you to beat the game within 920 jumps, and you can't check to see how many times you've jumped so far. To elaborate, you'll often need to jump several times in one place to get a high enough bounce, and then there's all the times you need to Wall Jump.
And then there's "&@♥@@p§☺A!○◘@)(@)_—-A" and "U KNO WUT I LUV", both with completely unknown requirements. There's currently no reported instances where anyone's gotten them legitly yet.
The Winter area features the most complex gimmick than the other areas. The platforms become solid (well, as solid as they get anyway) when you jump into one, and you can only pass through other platforms if you're currently touching the currently solid platform. Furthermore, these platforms are almost always criss-crossed over each other, and each one can also become inverse-solid in which the area outside is solid and the area inside is air. Due to how the level is laid out, it's extremely difficult to backtrack your way through after reaching the exit elevator, especially since when returning to the area later on it remembers what elevator you last left the area from. Fortunately, it's not too difficult to find the one hidden house here, so if you find it you don't have to worry about coming back here again.
Unwinnable by Insanity: If the player has the 100% Completion reward unlocked, and then travels to the very last secret area detailed above and uses the SET command inside the house to restore the jelly physics (or use custom values), it's possible to backtrack through a part of The Very Definitely Final Dungeon. If afterwards, the player saves and quits and then reloads the game however, the jelly physics will be frozen again as the custom jelly physics are not saved, leaving the player permanently trapped as they cannot get passed the room just before the one where the jelly physics first froze. Whoops! Thankfully, if you know where the save file is stored, you can edit the second value (which stores your character's X position) with a text editor, so that you reload on the correct side of the offending room.