Hi! I've just recently picked up the 1.5 HD version of this title and am currently working towards the speed trophy. Watching some runs and the excellent tutorial by Bl00dyBizkitz has really helped me through the first part of the game and I am now up to Halloween Town. However I'm confused as to why people defeat the Opposite Armor during the run as it is an optional boss. Is it because it is easier to defeat that than the Traverse Town portal at the end of worlds?

It's because you get the Aero spell from him which can save your live in the final fights

Ahh awesome thanks :)

Opposite Armor is not an optional boss and Aero has nothing to do with the reason for fighting him, it’s just a nice reward.

To unlock Hollow Bastion you need 2 Navi-G pieces. You get one from sealing the Neverland keyhole and one from sealing the Traverse Town keyhole (which happens after you beat Opposite Armor). Without beating Opposite Armor you can’t finish the game.

The only optional parts of the game are Olympus Coliseum and you can skip one of Atlantica, Monstro or Halloween Town since you only need to finish 2 of those 3 worlds to get Neverland to spawn.

(100 Acre Wood is optional too, obviously.)

(Dammit I forget that world exists at least once every few months)