Press A + B to do a special move. Note: This takes away a little bit of life. Press Attack + Down/Left. Note: This results in a different move for each character.
Choose Cyclops when selecting a character. He has no punch combo, so you can continuously punch one enemy till he is KOd without having to stop, unlike the other X-men who can only punch three or four times. Note: This will not work on most Bosses. mini-Bosses and Sentinels. Also, an easy way to complete the game is to use your points to increase your strength. Choose Cyclops, and as you complete levels, use your points on his strength. The game will be easier, and eventually your normal attacks will become stronger than your special attacks.
Knock Night Crawler onto the spikes that appear from the floor. Keep punching him, and the spikes will help kill him quickly, often without hitting you back.