The battle with Buzz, the ex-minion and now ex-bunny, is fairly straightforward.
He has six total health and three phases, transitioning to a new phase after every two damage.
First phase, charge him and he will jump to his right, just keep charging him.
Second phase, after hitting him with a charge he will create a ring of fire around himself after he jumps. Just wait for the fire to go away then charge him again.
Third phase, after the jump he will create the ring of fire for a second before shooting three waves of fire balls that you need to jump over. Dodge, charge, congratulations.