[toast0]

The SNES SF2 games have a similar-ish code for various things. I think the first release lets you enter a code to play the same character as both players, or disable special moves. Turbo has a special code to increase the turbo stars and you can also disable special codes.

[reassembled]

Before the Capcom logo and song finish playing on boot, enter the code: Down, R, Up, L, Y, B.

This enables both players in World Warrior to pick the same character.

Entering the same code in SF2 Turbo on the TURBO logo screen unlocks more game speed stars in the options.