I wouldn't be a MMX fan if I didn't mention some of the stages that could work in Smash either. Namely Central Highway, the GOAT from the first game.
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Since it has crumbling platforms, I imagine that's how the stage would be laid out, more platforms than Battlefield, but the "extra" ones crumble away and then re-spawn. Obviously they'd have some permanent ones as well. I could see some of the Bee Copters flying in the background too, without actually intruding on the stage.
The other stage choice I would go with is Noah's Park from Mega Man X8.
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It's a Jungle opening stage, which helps it stand out, since it's a lot of cybernetic plant life. And there's a section with a waterfall in it too. I don't know what I'd make the stage's gimmick, I just think it'd look great in HD.