The FC Caverns are a short series of areas accessible from several worlds, including the hidden passageway of the Techno Condominium corresponding to the FC Caverns A, a deeper zone in Zodiac Fortress corresponding to the FC Caverns B, and the green or red entrances in Color Cubes World corresponding to the FC Caverns C.
Features
The FC Caverns are an extremely unique area among all of the worlds in this game, as it plays out more like a movement-heavy platformer (such as Super Mario World) than a typical exploration-based RPG. Furthermore, if the Shift key is held down while in this area, a grid overlay will appear and time will slow down as if the game was 'lagging'.
Worlds
FC Caverns A
FC Caverns A is accessible from a hidden path in Techno Condominium. The world starts with two screens of red blocks on a dark background, ending with a door at the top of a tall wall. This door can be reached by using specific effects. Entering it leads to another section with a glitchy tileset that resembles that of Alien Cellar and a large pool of water. Making your way to the left leads to a long vertical section, where climbing to the very top will lead to a door to Flooded Dungeon.
FC Caverns B
FC Caverns B is a small section accessible from Zodiac Fortress. It strongly resembles the area preceding it and consists of a grid of rectangular tiles. Some of the tiles are solid, requiring the use of small effects like Child, Fairy, Grave or Dice to pass under. Using the Invisible or Grave effect will let Urotsuki phase through the hollow tiles. Navigating all the way to the right, you can find a dark corridor to Monochrome Feudal Japan. On the first screen, reaching the bottom part with the Invisible effect, and going under the very bottom-left solid platform with a small effect, then re-equipping either the Invisible or Grave effect under that same platform will lead to a pit with a doorway to the Hidden Garage.
FC Caverns C
FC Caverns is the section of FC Caverns accessible through Color Cubes World. Throughout the area there are several different colored cubes. Hitting them changes which colors are currently active and which can be interacted with. There is also a door here leading to a looping room akin to the ones in VVVVVV's Teleporter Maze. After heading into the other door here, an ascending vertical shaft awaits which eventually leads to a small corridor leading to outer space, which corrupts as you head outside. After the game "glitches" you will be sent to Home Within Nowhere.
Effect interactions
Almost all the effects have a different behavior in this area. While some allow Urotsuki to interact with the world in particular ways, others are purely decorative.
Effects with special interactions
| Effect | Sprite | Interaction |
| Bike |  |
Allows Urotsuki to move faster, but jumps slightly lower than with other effects. The bike does not slow down when not holding inputs once movement is began. |
| Lantern |  |
The flame inside the lantern gets put out whenever Urotsuki goes underwater. |
| Fairy |  |
Allows Urotsuki to float on top of water and to slowly elevate when in water. It also allows to fly outside of the water by repeatedly pressing the interaction key, and in addition allows Urotsuki to fit through spaces that are only one block tall. |
| Twintails |  |
Allows Urotsuki to jump against walls by holding the interaction key, along the key corresponding to the direction of the wall. In the FC Caverns C, can be used to toggle blocks by interacting with them from the side. |
| Spacesuit |  |
Can slowly float when in water and outside water by holding the interaction key. While floating, hitting the ceiling or an overhead block will cause Urotsuki to bounce off of it and float back down towards the floor. |
| Eyeball Bomb |  |
Allows Urotsuki to return to the Nexus by holding the interaction Key. It can't be activated in water. |
| Maiko |  |
Jumps lower and moves slower. |
| Penguin |  |
Allows Urotsuki to swim. Drifting is also much slippier than default, making Urotsuki behave like they are on ice. |
| Spring |  |
Allows Urotsuki to jump repeatedly by holding the interaction key, with every jump being higher than the last. |
| Invisible |  |
Allows Urotsuki to phase through semi-solid platforms. Although such platforms are only featured in the FC Caverns B, you are able to phase through the platforms created by Polygon and Rainbow as well. |
| Stretch |  |
Allows Urotsuki to stretch while holding the interaction key. When released, Urotsuki makes a small jump. Pressing left or right while stretched will make Urotsuki jump out of it, giving her a boost. May be a reference to the Uproot ability from Super Mario Odyssey. |
| Haniwa |  |
Allows Urotsuki to quickly sink in water, but it moves slowly and jumps really low. |
| Child |  |
Jumps lower. Just like the Fairy, can fit through one-block holes. |
| Trombone |  |
Plays trombone sounds instead upon attempting to jump. |
| Tissue |  |
Allows Urotsuki to fall slower underwater. |
| Polygon |  |
Allows Urotsuki to create a platform by pressing the interaction key while jumping. Doing it again destroys the platform. The platform's width varies depending how fast she is going, faster horizontal speed creates a wider platform. Falls slower while underwater |
| Teru Teru Bōzu |  |
Makes it rain. |
| Bat |  |
Allows Urotsuki to fly by holding the interaction key and pressing the direction keys. |
| Insect |  |
Allows Urotsuki to get stuck in some walls by holding the interaction key, along the key corresponding to the direction of the wall. Urotsuki jumps when the keys are released. Sticking to walls does not work while underwater, but Urotsuki is able to fall slower. |
| Drum |  |
Allows Urotsuki to float in water, and ascends much quicker than other effects while in water. Whilst underwater or floating on the surface of it, running into walls will cause Urotsuki to bounce off of them. |
| Bunny Ears |  |
Allows Urotsuki to jump higher and fall slowly, in a manner reminiscent of the Bunny Mario powerup from Super Mario Land 2. |
| Rainbow |  |
Running will create a platform under Urotsuki, which allows her to run in the air. It also makes the water's surface walkable, after Teru Teru Bōzu has been used to make it rain. Also causes certain rainbow platforms to appear upon being equipped. Falls slower while underwater. |
| Cake |  |
Urotsuki can smash the cake by hitting a ceiling. |
| Grave |  |
Pressing down key allows Urotsuki get to the down section. |
| Crossing |  |
Causes the flickering tiles to stop changing color, turning them completely red. |
| Dice |  |
Allows Urotsuki to fit in a one block space. Jumping causes the dice to roll, which behaves the same as it does outside FC Caverns. |
| Haniwa + Cake |  |
Behaves identically to Haniwa, except it sinks slowly in water. Urotsuki is stuck looking to one side. |
| Bike + Wolf |  |
Behaves exactly the same as the Bike effect. |
| Red Riding Hood + Teru Teru Bōzu |  |
Makes it rain. |
Effects with no special interactions
| Effect | Sprite |
| Boy |  |
| Chainsaw |  |
| Glasses |  |
| Wolf |  |
| Telephone |  |
| Plaster Cast |  |
| Gakuran |  |
| Marginal |  |
| Red Riding Hood |  |
| Twintails + Glasses |  |
Trivia
- The TV-headed NPC in the FC Caverns A and C appears to be a reference to VVVVVV, a platformer with a similar aesthetic to this area.
- Similarly, the former’s red-and-muted-pink color scheme of the area, as well as the overall glitchy aesthetic and 2-dimensional movement are highly reminiscent of the game Strawberry Cubes.
- The shift menu is automatically activated here, even if you disabled it.
- Version 0.119b Patch 5 contained a bug which allowed out of bounds exploration, which allowed players to see debug rooms, FC Caverns C (earlier than intended), and some other worlds yet to be released.
- From Version 0.119b Patch 12 until Version 0.119c Patch 2, the player could clip out of bounds by utilizing several effects in the last corridor of FC Caverns C. Upon doing so and heading directly left past the edge of the screen, a hidden door could be found, leading the player to Windswept Scarlet Sands. The connection to this area has since been moved to Static Labyrinth, the door was removed and the glitch to clip out of bounds was fixed.