Ill wait til I see the draw for proper tactics. Some basic tactics for now though:

Pussycat, Firestorm, T-Rex - KILL

Megaman X - If enemy has an easily identifiable weakness, use weapons to exploit it. If not, take in a variety and try various things. If in doubt use 4th armour and plasma shot.

Gravity - Bounce them around by changing the gravity in the arena very quickly

Nightmare - Uh, god knows. Whatevers cool

Count Dracula - If alive, feed. If not try and tear apart.

Pikachu - Throw the fight and get massacred. Cmon, you all know you want it