There's this really Chonky Heartless that you need to attack from behind to properly damage, or else you bounce back. Well, I hate them. They give a nice 10 EXP, if I recall correctly, but they're such a pain to navigate around. Whenever I'm not bothered, I cast my lightning spell to quickly get them over with.
Anyway, I sealed the keyhole to Traverse Town after a lot of grinding. In unlocking new worlds, I sent my gummi ship around to have them open up, but kept getting taken to places I'd already been. I'm starting to see why people disliked this part of the game, since they really streamlined the gummi ships in later games. Ah well, whatever.
My plan is I'll level up first in other worlds, then aim for around level 70-80ish by the finale. I'll probably go beat the game properly after beating the cups in Olympus Coleseum, beat the secret boss added in the Final Mix edition, then finally finally finally (search the secret ending online before) move onto Re:Chain of Memories!