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 and can be used from anywhere on the level.

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

The lava tunnel where the Miner's pod is located may spawn in the lava pit where the Cremator spawns.

Tactics
When fighting the Cremator the trick to dodging his damage is to keep moving. Try to dodge in the opposite direction of the boss, as passing through the stones he flings will result in you taking the damage. If you must dodge towards him, keep an eye on the arc of the stones so you can pass under them. When attempting to damage and kill him, use the platforms to attack him (try not to fall into the lava).