General: When OoB, you can exit the room in different places to warp to different rooms. What determines where you warp is first the cell you exit, and then what happens in the next rooms you enter, which may depend on what you do as you exit. Rooms are normally connected by one cell to another, with one cell being the smallest 1x1 room on the map. If you exit where the map shows an exit, then you will go to its connected entrance. But if you exit where there is no connected entrance, you will either warp to some other entrance, or the game will hardlock. Exiting a room from the wrong place will often warp you inside a wall. Depending on what you do when you exit, this means different things can happen when you are inside the wall in the next room. By using these different possibilities, getting OoB gives you many different potential warps you can do.
Immediate Room Warps: When you exit a room the wrong way, sometimes that makes the game place you already off-screen in the next room, so you warp again immediately. Also with a little vertical difference as you exit a room OoB, it may take you above the next room or below the next room, so that it will warp you to different rooms. This usually means being higher takes you below the next room, and being lower takes you above the next room.
Diagonal Warps: When OoB, you can exit the room horizontally and vertically on different cells to warp to different rooms, but you can also exit diagonally. This is much harder and less consistent than the other warps, and divekicking down into a corner is usually easier than jumping up into a corner. This happens in the OoB warp Maxim uses to get from the Top Floor A OoB to Sky Walkway B OoB in the less optimal Any% routes.
OoB Wallrides: When OoB next to a wall with a screen below that sends you back up to the same room, if you are close to the wall and face away from it as you exit the room downwards, you will reenter the room inside the wall and be zipped upwards.
Actions While Zipping: (Sliding) By positioning yourself at the edge of a room as you zip up a wall, you can slide out of the room into another one.(Dashing) Inside a wall, you can whip and cancel the whip by dashing. It doesn't give you the same speed as sliding, but it can be repeated more often. Usually it doesn't let you move horizontally by repeating it, but in rare cases it does. I think you have to be inside a wall just enough so that you can't quite slide out, but you're still close to coming out of the wall, so that dashing out of it twice works when sliding out would not.
Horizontal Wall Pushes: (No horizontal movement) Divekicking, falling down with a whip out, and sliding into the next room (and other actions like that) will put you firmly into the wall, so you zip upwards.
(Get pushed backward) Jumping in normally will make the wall push you back in the opposite direction of the one you're moving in. This can be used by making a horizontal screen transition into a room where you start inside the wall, so the wall pushes you back to do another warp to a different room. It seems to work better and prevent hardlocks if you exit the room at slower speeds, and if you're moving downwards instead of upwards in the jump. (Get pushed forward) Similarly, if you change direction the frame before you exit the room OoB, the wall in the next room will push you a little further in. This can let you slide out when you otherwise wouldn't be able to. It's used to get the summoning tome from the box-zip.
Downzips: If you're moving vertically upwards at a low speed and touch a ceiling, the game pushes you downward. This is normally how you hug the ceiling while whipping in a jump as Juste instead of bouncing off the ceiling. But if you do this in an OoB screen transition into a wall, it will make you zip downwards for a little while, before zipping you up. It can be used both by a vertical screen transition and by jumping into a horizontal screen transition. Down-zipping is more effective when you have moon physics. Unlike Juste, Maxim can't down-zip with his air attack. He can only down-zip a little during his roll. (Diagonal down-zipping) By holding forward while down-zipping with the whip, the wall will also push you backwards, so you will zip diagonally down and back.
Floating Boots While Out of Bounds: With Juste's floating boots, you get a lot of extra things you can do inside walls beyond warping into them differently. Zipping into a wall by launching won't let you use these, so most of the time you have to do it by OoB. You can also whiplaunch and then switch to floating boots to preserve the speed of the whiplaunch.
Floating Boots vertical movement: If you have downward speed with the floating boots in the wall, then you will land and start crouching. By holding Up, Juste will normally in the air move upward slowly, but in the wall it will push Juste downward slowly. Normally in the air if you're not holding anything, Juste will move up and down in the air. If you go into a wall at the time he's moving up, then the wall will push Juste downward faster, like a down-zip.
Walkway/Aqueduct A --> Merman Boss room A
Aqueduct/Cavern A --> middle of Cavern A (two rooms to the right of save)
Clock tower/Walkway A --> top of the second Chapel B room from the Walkway entrance
Cavern/Treasury A --> merchant of Treasury B
Walkway/Aqueduct B --> Merman Boss room B
Clock tower/Walkway B --> top of vertical shaft connecting ball race room and clock tower A
Treasury/Skeleton Cave B --> next screen of the skeleton cave B
Aqueduct/Cavern B --> middle of Aqueduct B
Cavern/Treasury B --> black screen
Treasury/Skeleton Cave A --> black screen