Big headed players
Wait until 'Press Start' flashes on the title screen. Press Top C, Top C, Bottom C, Bottom C, Left C, Right C, Left C, Right C, B and A. Press and hold down Z, then Press Start. The announcer will cry 'Goal!' Big heads will not appear until you actually begin a match.
All-Star Teams
Wait until 'Press Start' flashes on the title screen. Using the Control Pad, press Up, L, Up, L, Down, L, Down, L, Left, R, Right, R, Left, R, Right, R, B and A. Press and hold down Z, then press Start. The announcer will say "What an incredible comeback!" In Open Game and Penalty Kick modes, you'll see a seventh group of teams -- the All Stars, comprising Euro Stars A, Euro Stars B, Asian Stars, African Stars, All American Stars and World Stars.