Good game with great mechanics! I think that it would be good to have some indications to where the enemies are, like some sound queues or effect before the player is attacked by them, and like the other comment, some sort of damaging indicator would be great.
Viewing post in Mr. Macbeth's Cave Adventure jam comments
The enemies actually make sounds when they notice the player, but maybe that's not enough because you still won't know where they will come from...
As for the sound queues, the dark enemies instantly attack you whenever they are close enough, so I don't think a sound queue will be possible. Just be careful when you push these bouncy ball reincarnations into walls because they are going to bounce back and give you a surprise.
I'll consider making these enemies mid-to-late game elites when I make it into a full game :p