Plexal Upstairs

Plexal Upstairs is an area in B3313.

Description
The area bears a resemblance in structure to the Vanilla Upstairs, with a top and bottom floor. In the top floor, there are two side hallways, which contain doors and paintings, the right one having a slope with a double door at the end leading up to the top floor, which has light blue walls, and a crescent above one of the doors, similarly to the Crescent Castle. Another upwards slope leads to a double door at the end of it, the highest point of the area.

Origins
The area's layout appears to be an original creation. Most of the textures originate from beta versions of Super Mario 64.

The music playing is the "Inside Castle" theme from the same game's OST.

Leading here

 * Collecting a star in an area without a painting entrance with the ripple effect (as of 0.9) results in warping to this area by default (with the exception of some unique cases, like the Bob-omb Village). This usually spawns the player into a darker version of the area, now located in Slide, with the music also changed into a minor scale, but the warps are unchanged. One possible effect of the Yellow Switch is to cause even the levels in paintings to warp you here after collecting a star, the default behavior prior to v0.9.

Leading away

 * Big Boo's Fortress: On the top floor, enter the door in an opening with the number 3 on it and a trap before it, then go down the hole and enter the Boo painting.
 * Creepy Cove: On the bottom floor, jump into the Jolly Roger Bay painting right up ahead.
 * Dry Town: On the bottom floor, enter the Wet-Dry World painting in the left side hallway.
 * Forest Maze: On the top floor, enter the door in an opening with the number 3 on it and a hole before it, then go down the hole and then the hole in front of the Boo painting.
 * Lavish Lava Mountain: On the bottom floor, go through the bricked door in the right side hallway, and then jump into either small painting of Lethal Lava Land.
 * Piranha Plant Garden: On the bottom floor, go through the bricked door with no number on it in the left side hallway, then jump into the mountain painting.
 * Pleasant, Pleasant Falls: On the bottom floor, jump into the painting of the abridged mountain found on a wall of the left side hallway.
 * (v 0.9) Forgotten Falls: Jump into Pleasant, Pleasant Falls painting in darker version of Plexal Upstairs. There's some random (seemingly) chance that you will be warped into Corrupted version.
 * Rainbow Ride (beta): On the top floor, jump into the hole in front of the door with the number 3 on it.
 * Sky-High Pathway: On the bottom floor, go through the single door at the end of the right side hallway, and then jump into the hole.
 * Uncanny Courtyard: On the bottom floor, go through the hole in the wall to the right of the Jolly Roger Bay painting.

Two-way

 * Beta Lobby B: On the bottom floor, go through the double door at the back and then the next one at the end of the hallway.
 * Cryptic Hideout: On the top floor, go through the double door with the crescent above it.
 * Plexal Hallway: On the bottom floor, go through the bricked door with the number 1 on it in the left side hallway, and then go through the double door on the other side of the mirror.
 * Underground Passageway: On the top floor, go up the slope and through the double door at the end with the Bowser painting above it.
 * (v 0.9) Royal Lobby: On the bottom floor, go through the double door next to the Dry Town painting.

Trivia

 * There exists two versions of Plexal Upstairs, a brighter version and a darker version. Travelling to the Plexal Upstairs by foot by entering via Beta Lobby B, Cryptic Hideout, Plexal Hallway, or Underground Passageway will take you to the brighter version. The only way to enter the darker version is by collecting a star as most of the stars in the game will drop you off in the darker Plexal Upstairs with the exception of a few stars that drop you off elsewhere. Leaving and reentering the darker Plexal Upstairs will take you back to the brighter version. There is no known way to travel to the darker version by foot. However, for whatever reason any star collected in an area that is within Course 11 will drop you off in the brighter version instead of the darker version. These courses are Chief Chilly's Ring, Chroma Tundra, Cold, Cold Crevasse, and the Course 11 version of Snow Slide. These are the only known courses in the game where collecting their stars drops you off in the brighter version as every other star in every other course normally drops you off in the darker version. There is virtually no difference between the darker and brighter version other than cosmetic appearance, all warps work exactly the same.
 * In v0.9, it's even harder to reach the darker version, as painting levels typically exit through the painting when collecting a star instead, (Though this only really affects the painting levels) However, it is possible for this feature to be turned off by pressing the Yellow Switch. (The feature uses Unused Flag #3.)
 * Although can get into the dark version if enter the Royal Lobby and then exit it again.