Street Fighter II': Special Champion Edition/Hidden content
From Sega Retro
Select character twice in group battle
Usually characters can only be selected once in group battle, and cannot be shared between the two players (e.g. you cannot have "Ryu vs. Ryu" mirror match).
This can be partially circumvented on the Battle Mode Select menu by inputting the following button combinations on the second control pad:
(if using a Six Button Control Pad).- (if using standard a three-button pad).
This will allow for a character to be selected twice, allowing for both mirror matches and for one player to have the same character twice in one "group".
References
