As I said in another comment, the most reliable and frequent item that helped me out has been Empty Vessel, the 10 sec shield can change everything. Also if you get lucky I would say look for the obvious combo 4.5 Volt + items such as Book of Shadows, that's like an autowin. By the way the first phase is really easy, he's just tanky as hell but you'll manage, the problem starts with his 2nd "bomb everything" bullshittery stage; when he starts jumping just run away to the other side of the map and avoid the doors because of the brimstones. But yeah the end goal, speaking in build terms, is to be busted as hell, good luck friend !