Oh, sinspawn Gui (ah, memories). To beat it, start out by using Wakka and Lulu t destroy the head (If you have second level spells, they work wonders). After the head is destroyed, bring in you strongest characters to destroy the arms and attach the body. After that, you have to fight it again but it is insanely easy. Afterwards, you go to the djose temple.

And no, its always the same sphere grid.