First, you have to get the Bethasar Nu to send the three Poyozo Dolls up to help you. Then, when climbing up, RUN and talk to the doll. It'll transform into a tree. Stay behind the tree until the wind dies down. When it does, run to the next tree and get behind it. It usually helps not to hold the B button when waiting behind the tree and moving up.
You MUST have either Magus, Marle or Frog in your party (I prefer Frog for this one). DON'T TOUCH THE CORE unless you are at a god-like state. Cast Water or Ice on either the top or bottom half, then attack a couple of times, then repeat. Stay on one half until it dies. Destroying the core will cause the Retinite to run amok and kill you. Having Shadow absorbing armor helps a bit here
The key is to not hit either hand at all. Hence, you should stick to single attacks, such as Dark Bomb, Fire Sword 2, Ice Sword 2, and the like.
Useful things you can steal-
Gold Stud- Steal from Flyclops, Black Omen
Speed Tab- Steal from Panel, Black Omen
Haste Helm- Steal from Lavos Spawn Head, Black Omen
Safe Helm- Steal from Lavos Spawn Shell, Black Omen