What can you do after you get up to ansem in Kingdom Hearts

There are optional bosses:
neverland: shadow- talk to tink in one of the cabins and she will take you to the clock tower CAUTION!!! very hard boss
Agraba (sorry about spelling) talk to the rug in aladins house it will take you to the desert CAUTION extremely hard boss
olympis collisium-sephiroth- talk to Phil chose ???? (later to be platnium match) CAUTION impossible boss took me days to defeat him