The name wasn't something I considered at all before uploading it on itch.io and at first I just called it "Only Once", however it wasn't going to be the only game named that, so I picked the first thing that came to my mind. As there is only one stage where I didn't avoid getting hit and every character is done in one touch it seemed appropriate.

With the enemies there wasn't a lot I felt I could do in a short amount of time. Had they just stood around it would be boring, had I made them avoid you it would be needlessly frustrating. By charging at you some stages turn more into puzzles instead of a simple platformer.

The movement would seem to be a preference thing. Personally, I strongly dislike velocity based movement as the character doesn't stop the moment I let go of the key. If there is nothing in the way the character in my game moves at a constant rate as long as you hold down the key. 

Jumping and falling (including knockback) is the only thing using velocity and the character once again stops accelerating upwards the moment you let go of the key. I'm not sure if this is what you considered the bug or if it's something else, however the only problem I encountered was with the first jump after acquiring the double jump, which didn't feel high priority considering limited time.