I’ve only seen 1 enemy, and it dropped 10 coins. Stage 16-10 on hard mode (the only one with Aemonna as the boss). Looks exactly like the little seahorse thing in the image here: Version 21 Release Notes & Status
It was a yellow enemy as well.
I did not screenshot unfortunately because I had just woken up at 6am (my dogs wanted to go out) and I hadn’t had coffee… but so far it’s just been the one I’ve seen.
EDIT: Got one again!
Stage 17-2 normal mode. Thus proving they appear both in hard and normal mode.