After defeating Ash in the game, he can be unlocked by holding A until the next stage begins. He will show up as a selectable character when the player uses a continue. His moveset is limited, and he has very little range, though his attacks are powerful. His best offense is to use grabbing/throwing moves. You can still see him in the American versions.
Ash wasn't completely removed from the American and PAL versions of the game. With the use of a cheat device such as a game genie or action replay he is still playable, however there's no code to restore him as a boss.