Help FFXIII: please help me

It'd be a good idea to reapply buffs the moment he restores his HP. Try and have one or two attack paradigms with a Sentinel in it, to reduce party damage. I'd also suggest switching to your healing Paradigm (preferably Combat Clinic, though Salvation works too) if your HP drops below 40%

Lastly, only switch to a Saboteur oriented role when he's on the ground, as debuffs etc don't work when he's in the air.
 
If you're having too much trouble then DON'T stagger him...

After his Stagger ends, he'll go into retaliation mode and that's usually what leads to people getting killed. The fight will last a little longer, but if you're perfectly ok staying alive whilst he's in his other two regular modes..then you'll be able to get through it.
 
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