Back in high school, a friend and I wrote a 3D platformer akin to Mario 64[1], including writing the engine from scratch. No surprise, the physics was by far the hardest part and we never got it quite right. There was one build of the game where I screwed up the jump button function such that if you held the button down while going up a slope, you would repeatedly make contact with the slope and perform another "jump", infinitely increasing your velocity until you hit the top of the slope. Then you'd go rocketing across the map until you slammed into a wall or something. Much like Tribes skiing. It was great fun and I kept a special build of that around for a long time until it sadly broke because we changed the level data format. This was before I understood source control so I was never able to get that feature back. Anyway good times. Great educational project, but that happy accidental jump feature was probably the most actual fun in the game.

My friend later went on to commercially release a 3D platformer, Poi. http://www.poi-game.com/

[1] Enjoy some high-school-student-in-2005 web design and writing, https://www.brightnightgames.com/games.php?game=sa&sec=devel...