Mega Man 6/X Fortress 3

Double-sided platforms are introduced in this level. Standing on one end will cause it to sink, while the other end rises (does this remind anyone of an old game called Super Mario Bros.?)

For most of this stage you'll want the Rush Jet equipped; it's much easier to use it than the platforms in many cases (and you can use those as safe landing areas to recharge your jets.) Just destroy and dodge the enemies that try to knock you into the bottomless abyss that fills so much of this stage.

The boss is a Hard Hat piloting a mecha. And he's not much tougher to beat than a regular Hard Hat. Whip out the Blizzard Attack, and put the machine's circuitry into a deep freeze. You'll probably have this fight won in mere seconds.