Barthandelus

After several days, I got rid of the upside-down choir. Now we've got the bad boy himself to deal with with Team Lightning, Snow and Vanille.

Part 1. The Choir

Ruthless (commando, ravager, saboteur)
Combat Clinic (medic, sentinal, medic)

Part 2. Laughing Boy

Ruthless
Combat Clinic

Yes, that's the same as before. Stay sharp about Destrudo and make sure you're in Combat Clinic well before that strikes. Mix in an occasional Relentless Assault, Solidarity, Diversity or whatever, but don't get carried away. Time is of the essence! Develop a major sense of urgency immediately. Strategy here is to stagger this clown at least once, maybe twice, and get his green line down to about 1/4 normal.

Then hit him with Odin. Watch your purple line, and whatever you do, don't bring on Odin until you've got a good chance to finish off Barthandelus with Sleipner!

Piece of cake, but unfortunately I survived with only two stars. Now on Chapter 10, The Fifth Ark

The only other advice I could add is Concentrate! Once you've won this scrimmage, it'll seem easy, but it's still kind of a high water mark for nasty bosses.

Chapter Ten, by the way, unlocks some nice rewards just for being there. Sweet!