I just use the Floating Continent. No Triangle Island, no Sealed Cave, nothing but good ol' Floating Continent.

The Ninjas mentioned earlier are easier to beat when you have Shadow throw Bolt Edges at 'em, they go down pretty easy. Those, and the Bedpans...err, Brainpans, I mean. They suck, but again, Bolt Edges do pretty well. Just go through it a couple times and it'll get pretty easy, then proceed when you're ready to go.