Hmmm... I don't know if you need to worry too much about a design doc. I mean, what you have right now is an excellent starting point for a prototype. Your code may be very messy and difficult to manage in early stages but it's inevitable that you'll have to rewrite and revise it near the end, anyway. Over planning at very early points can be a real drag on production and function as a distraction. Trust me, I know this from experience.
I'd say you have the seed of something really good. I noticed you have a lot of marked triangles that seem placeholders for ramps Do you have those working now?
Hey, Thanks! The triangles are actually Castlevania-style stairs! They kinda work, but I will rewrite them in monogame eventually anyways lmao
Okay, I will not worry so much about the documentation then! I am happy that people are liking it
By the way, here is the camera system: