Achieving 'flight' in vanilla, Boom etc.. A new technique?

Hey there! I'm writing this post to share a technique I discovered in 2022. May it bring mapping joy to those that are interested! I was fiddling around with Mikoportals and realised the player can achieve stable 'flying', including the ability to change directions while in fly-mode, under certain conditions. This kind of flying can be done in vanilla, limit-removing, boom, mbf21 etc.. It might even be done in GZDoom, when using custom frictionless flats, but I haven't experimented with that. (shoutout to the good folks of NERF, that used frictionless flats to great effect in their map set for vanilla conveyors)

Here's a video of an early experiment of mine incorporating 'flight'. (music by @Napsalm) Video with an elaborate example at the bottom of this post.

So what is this? We know that when a player falls onto a floor with a height of -32768 units, the player's vertical position is instantly changed to that of the ceiling, while maintaining momentum (more info on Mikoportals over here and here). Because of Doomguy's lack of air control the player loses all ability to manoeuvre once they fall unto a sector with a -32768 floor. As you can see in this video: the 'falling' that occurs when you enter a Mikoportal appears to stop after a while, seemingly attaching the player to the ceiling ('flying') while maintaining momentum. This by itself can be an interesting effect, if limited. It's been used by many people to create 'vanilla conveyors'.

The 'flying' effect persists when the ceiling height goes up, regardless of the floor height below. So a player can fly upwards if the mapper wants them to. Flying down is not possible: any ceiling lower than their current one will halt the player. Once the player is 'airborne' and has flown up a bit, the floor below the player can be higher or lower at will and the effect will still persist. This means you can make arenas with varying floor heights: not just a straight monotonous hallway. Note: during testing the flying effect sometimes stops when doing this too quickly after achieving flight. I recommend waiting a few seconds until stable flight has been achieved, before changing heights.

Some visuals:

Now the fun part: once the player has gone up a bit in terms of height, the floor can be raised upwards until the height of a sector is 56 units (Doomguy's height). Upon entering a sector with this height, the friction of the floor will slow down and halt the player. The player is able to turn, accelerate and all that jazz, as if walking. Think of it as you dangling from the ceiling by your helmet, and your feet being able to touch the ground and push you around. The flying effect persists and will kick in again as soon as the floor lowers again, even a tiny bit. This means the player only needs to set up the flying process once, and after that they can enjoy a whole map mixed between flight and normal running.

Some more visuals:

I made two serious maps in 2022 and 2023 that use this effect. One for Twofers in mbf21 (released today, that's why I'm posting this thread today. Have a look here: MAP17) and one for my own limit-removing Ultimate Doom project (to be released SoonTM, video below). I also experimented with various other ideas, such as a vanilla compatible pinball machine and other scenes. I am sure there will be some mappers that can do lots of cool creative things with this technique. Looking forward to what others cook up with this!

Some interesting observations:
-Blood 'falls' upwards upon a monster's death on a floor with -32768 height.
-Projectiles 'fall' upwards when hitting a floor with -32768 height. A rocket exploding on the floor will have the exposion fall upwards as well.
-Monster death sprites that fall (like a Cacodemon) will sometimes start bouncing like a voodoo doll and at times they even achieve 'stable flight'.
-A walking monster (like an Imp) that starts on a floor with -32768 height and then walks upwards, will sometimes start flying themselves upon touching the ceiling. Including all of the initial bouncing. Have a look here for that.
-Monsters can hit the player during flight, changing the player's direction. I think there is a wealth of effects to be explored there, with things like chaingunners or custom dehacked monsters hitting the player (with or without an Invincibility Sphere) and moving the player through a space. Perhaps custom mbf21 projectiles that just move and don't hurt the player? Invisible even? Having one custom dehacked gun that fires non-hurting projectiles behind the player, propelling them forward? You could have a whole map set like that, with ammo for your propulsion being in short supply. Jumpwad but Flywad. The fire extinguisher scene from the movie Gravity, who knows? (right now damage is tied to movement so this is limited, but still) Video of Napsalm experimenting with this (early rough version).
-I haven't experimented with Wind Sectors in Boom yet, perhaps those work to move the player around?

Some thoughts, ponderings:
-Perhaps this has all been done before. Please let me know if any 'serious' maps have been made with this effect, that would be interesting. (If I really am the first, do I get to name it? I was thinking 'Mikoportals, Linguortals: Peccaportals'. Mikolah suggests 'Peccombat' and muumi proposes 'pecca-flight')
-The only way to stop this effect once flying has set in, is teleporters, as far as I know.
-Right now my setup is a quite long, straight hallway. This could probably be made quite a bit smaller.
-Infinite vertical height still applies to monsters, so flying over the head of Imps is not possible. I assume some entrepid MBF21 people will probably be able to dehack Things to make this possible. Looking forward to maps with the player flying over the heads of monsters while fighting them :)
-In these two maps I made, there are quite a few places where the player can softlock. They can get stuck against a wall when they launch and haven't aimed well, or get pushed by a monster. A way to 'fix' this is including a 56 unit high ring around any flying area. This can both be done in interior areas, or in areas with sky flats. Not the same but kinda like chosing to have inescapable deathpits or not, I guess.
-Would be nice to see a map that has the player return to the same area a couple of times, where the ceiling changes height each time, giving way to a new experience in the same location.

Finally here is a video of a map from my upcoming limit-removing cl3 Ultimate Doom map set. The secret map in that set is centered around this type of flight. [SPOILERS!]

Big shoutout to @Mikolah, @Linguica and all the others that have discovered/explored these tricks. Doom mapping means standing on the shoulders of people, that stand on the shoulders of even more people. I'm grateful for all the creativity that is shared by the people of this community.