I really like the idea of two sides of your character having different attacks. Art needs work but not everyone's an artist so I'll let that slide. Music is pretty good, too.
My main problem though is the gameplay. It's nearly impossible to tell if you're doing something since there's no animation when anything gets hit, and the ninja slime boss spawns too often, I think.
The real issue is that the game slows to an unbearable crawl after a few seconds. I had this when I was making my arcade Kaiju game a while ago, and that was because by accident I wasn't deleting the player's projectiles that went offscreen. Maybe you keep infinitely spawning slimes/terrain/projectiles and not deleting them when they aren't visible?
Overall, this game definitely needs a lot more polish, and I can see a core of an interesting game here!