Tiny characters: It is possible to fight a miniaturized opponent in VS Mode, only against CPU. Just select him by hitting B.

Chibi Mode: Just before the stage appears, hold A+B+C+D, and enter ↓  ↓  ↓  ↓ .

Play Gokuu: On the character select, hold C, then enter ↑ ↑ ↓ ↓ ← ← → → + BC.

Play Neo Dio: On the character select, hold B, then enter ↑ ↑ ↓ ↓ ← ← → → + BC.

Play Zeus (Neo Geo CD, VS Mode): On the character select, hold B+C+D or A+B+C until he appears.