Ultima-Griever
Sorceress
Jesus Christ. Whoever came up with the idea of creating the Great Crystal was insane and wanted the players to go insane, too. The only time I had no difficulty going through it was on the first time I got there: of course, because there is only one way you can go: to the Crystal Core. But when you go upwards, either to get Ultima and/or defeat Omega Mark XII, it's nearly impossible to go through without a freaking map. I don't know if it was only me, but I was stuck at the Great Crystal for nearly 4 hours and a half, completely lost, until I stumbled upon Ultima. Thankfully my party was in a high level, mainly due to the monsters inside the crystal, and I defeated her in a single fight. Then again, to find Omega Mark XII - another torture, and I was even looking at a map. That background music is annoying and so is the noise of the party running around. I wish I can never ever do anything there again, I don't even feel encouraged to find the Zodiac Escutcheon there. ):