Lightning Returns: FFXIII: Bhunivelze Fast kill/Farm guide [Normal 5*/No DLC] 

First form: Stagger and overclock-kill him before he recovers.
Second form: Get rid of his Monad's before he unleashes Wings of Destruction because they will explode and do additional damage, it seems like the damage done ignore all resistances as well. Also, kill him before he uses his charging skill. Alternatively, you can try to stagger him right from the start.
Third form: Try to stagger and kill him asap again.
Final form: Stagger him by spamming -ra spells, overclock is needed. Try to stagger him before he uses his angel skill.
Tip: Remember to equip Beggar's beads before entering the boss fight for increased chances of getting an item. It can be found in Poltae near Rocky Crag in the Wildlands.