This is a cool idea. It's surprisingly hard having to click super fast while tracking the heart. the game is simple but it's surprisingly fun. I think I beat it, but the ending seemed to be the same regardless. It would be really nice if it said "You Won" or something. But beyond that, the game is cool.

In Undertale, almost all the projectiles are telegraphed by being spawned outside of where they can actually hit you. If you could only spawn attacks from outside the box, that would then target the heart then:
1) the heart can actually dodge it in a logical manner.
2) you, the player, would have to figure out what combination of projectiles will actually give the heart nowhere to run to, so you can actually hit it.

A nice idea, but could get more love in terms of mechanics. Still pretty fun to watch as player tries to hide :D

I loved undertale, it is a fun game, although it could have some more components and I don't have a clue when I am attacked, it's pretty fun :3