I can see where you were going with this. I have tried the web and downloaded it. I found that sometimes mobs spawn and immediately knock you off when you spawn, sometimes mobs spawn behind the starting point, and sometimes when you survive long enough the platforms just disappear.
I would maybe consider having some kind of decay on projectiles, because sometimes you see them coming at you but you don't come across an enemy for a very long time (maybe they are just killing each other before you get there idk).
good job.