Ok, I havent been online for a little while so I haven't beat him yet but I do know how to here is the list of stuff.
Hat- Volcanic Mask (suggested)
Robe- Brimstone Tunic(suggested)
Boots- Cinder Shoes(suggested)
Kill the minion first
Try to get critical
Polymorph to the tree mainly.
The main thing is to have a good fire resist so if you can find a hat/robe/shoe with a high fire resist rate and critical that is the stuff you need to wear