I based this design around the Wanyudo, a demon from Japanese mythology that takes the form of an eternally-burning spoked wheel. In some iterations, anguished spirits are trapped inside. It guards the gates to Hell. Zav's character is able to use fire, so I ran with that theme.

Boss: Zavryn

Attack Style: Zavryn is the size of a giant, and his wheel is even more massive - to attack, he steamrolls over the player, impaling them on the spokes and inflicting a lasting burn. His stage is markedly placid - a landscape scene - and he presides over it with care. Anyone who dares enter his territory will incur his wrath.

Speed: Fast
Range: Close
Hits: Medium