Here is another community project with a silly premise for mapping constraints. It's titled "Alphabet Doom", a 32-level megawad for vanilla (limit-removing) Doom 2 where each level must fit within the outline of a letter!
Download now from idgames! https://www.doomworld.com/idgames/levels/doom2/Ports/megawads/alphabetdoom
For example, Map1 which is the letter A:
* Map List & Credits *
MAP01: "Arachnophobia" b