Nice particle effect while absorbing the enemies holding B button (X on the keyboard), and I think it can be replicated on an actual gameboy.
The 4 selected colors fit the mood very well.
The giant eye monster in the background that opens and closes the eyelid is a very interesting and impressive effect.
Note to other players: if you walk all the way to the right, you'll find a cliff. avoid falling into it, as you'll have to wait until your health deploys until losing and being able to play again. There's a cliff to the left after walking a while too. Didn't try jumping into it but I guess the same would happen.