Whats this boss called ?

[BG-57]

The boss in the cave thing, the one that keeps changing its element type ?

Do you need a strategy for defeating it? Or are you just interested in the name?

[ff7+ff10 gurl 100]

Maybe a little of both

[BG-57]

Hit it with an attack every time it changes its element and it will counter with a spell of that element. Pound it with spells of the opposite element until it changes again. Rinse and repeat.

Avoid elemental weapons unless you feel like changing weapons in mid-battle.