[New feature]: Magma Cube!

[dyanakiev]

I played moded minecraft today, and in one of the mods when u break dirt and grass at random % is spawning small magma cubes.

[RoboMWM]

Sounds interesting... But wondering how much sense this would make. There's already another idea to make shulkers naturally spawn in ravines and potentially caves, so that's interesting. But trying to think of a good element this provides other than "surprise, random mob spawns in your face!"-type deal.