To activate the Big Heads option in the Extra Options menu you must fight 100 matches in Arcade or Versus modes.
Honey's Bonus Outfits (Japanese version only):
Defeat the game on very hard setting in arcade mode. These outfits are selectable in VS., training, and team battle modes.
You must successfully perform 350 moves in training mode to get invisible walls selectable in the options plus menu.
Options Plus Menu:
To access this menu, you must beat the game on Normal mode or harder with any character.
Play as B.M.:
To play as the last boss, Big Mahler, you must win the game on very hard with any character. B.M. is only playable in Vs. mode.
Play as Kumachan:
To play as Kumachan the Bear you must fight 50 rounds in Arcade or Vs. modes.
Play as Mahler:
To play as the smaller version of the end boss, you must beat the game with any character in normal mode.
Thanks to Revolution reader Thomas Wisdom!