Most Hardest Optional Boss

[Goldenboko]

He attacks one time and my party is wiped out and most of my characters are in level 20's with Squall being 38.

Levels don't matter in FFVIII, junctions do, magic is incredibly easy to get, get your junctions a bit better, his first attack his really his worst attack out of all of them (with Terra Break you can at least use defend to block)

EDIT: Even so, you told me what level you fought Omega (which is decently low), but you haven't told me what level you fought Ozma at. I can't imagine fighting Ozma in the 20's >.<