-Thank you for your comment! First of all, optimal wall-jumping is hard to code, but I'll try to improve it.
-I don't think you need checkpoints because the levels are so short and you have a lot of lives, but I can understand it being frustrating to some players.
-The teleporters work that way so that you don't tp yourself if you don't want to, though you're not the only one complaining about this issue.
-You have to know by heart the 3 attacks of the boss, and adapt yourself accordingly. I feel like the boss is easy enough, and it'll be even easier with checkpoints.
-I'll try to fix all those annoyances in a big future update (i'm working on another game right now)!