Okay, then you're in a pretty good place level-wise.
The big key to that boss is have Porom cast Slow very first thing. Tellah and Palom should be casting Blizzard spells (highest level you've got), and Thunder if the boss calls the water around him, which will dissipate it. I got lucky and took him out without him really doing much of anything to me in those same levels.
The next dungeon after this, you'll probably want to power up to mid-high 20s or around 30; the one after, I was wrecked until the high 30's, just for reference's sake.
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The big key to that boss is have Porom cast Slow very first thing. Tellah and Palom should be casting Blizzard spells (highest level you've got), and Thunder if the boss calls the water around him, which will dissipate it. I got lucky and took him out without him really doing much of anything to me in those same levels.
The next dungeon after this, you'll probably want to power up to mid-high 20s or around 30; the one after, I was wrecked until the high 30's, just for reference's sake.