For the Super Nintendo game, you have to input a cheat. When selecting the character, leave the picking cursor over Tallgeese and press L, L, L, L, R, R, R, R, L, R, L, R, L, R, L, R. Then the game should automatically choose Epyon.
Depends on what series you are watching. In Gundam Wing, gundams are just mobile suits made of Gundanium (sp?). In Gundam Seed they were mobile suits with phase-shift armor (or something like that)....