Cremator

Only spawns in the Magma Barracks.

Shoots a random shotgun-blast-like-spread of bombs with the white circle, much like the Wandering Vagrant's attacks to show where they'll hit.

This attack is easily dodgeable, but can hit you on the way up to its target zone.

He spawns swimming in the lava at the bottom of the map like a giant turtle.

Unless you possess a non-linear attack you pretty much have to swim in the lava to kill him.