Simple cheat, go to the power station in multiplayer duel mode, you acn also try this during the game, when you are fighting an opponent. You will see a large circular platform that shoots up this energy, with a field that does dmg to your health and lifts you up and throws you back. Now if you played the game in this area for the storyline you know that the characters heal over these platforms, you should consider, why is that? Simply put it heals you, and I'm going to show you how. First, choice a character that flys in place: magneto, storm, johnny ohms, etc. When you see the rings appear on the floor and the machine starts to charge up, makes sure you fly exactly center over the platform. You should be in the air at at the very top touching the ceiling above it, when it fires off. You will notice that if you had dmg take to your health before, you will heal afterwords, it does knock you out after wards. If you realized you don't heal 100%, you did something wrong, or you got stuck in the energyfield a little to long during the knockback effect it produces. This will result in healing 3/4 of the way or even to the point where your only missing a small amount of your health. I use this when I duel, and my friends don't know how I do it, I just fly over the center, and heal myself. By the end they are begging for life, but there isnt any for them to find.

During the level PowerPlant, in versus mode you all have seen the energy field that shoots up from the center of the room. Now wait in the center when it is shut off, and watch for the rings too appear on the ground or the sound that it is starting up, before it starts up, fly all the way straight up to top of this, staying in the middle of energy field. Whne it shoots you, while your flying it will heal you completely, and spit you out. If your not exactly centered while flying or you too low when it fires at you in the air, you will heal almost fully, but you will still be missing a little life. This works in the versus mode, and as far as I can tell it works in the story mode as well. Free health, who can pass that up?