Two-player mode with same character:
Quickly Press Down, R, Up, L, Y, B, X, A at the Capcom logo before it disappears. The title screen will flash blue to confirm correct code entry.

Ninety-nine continues:
Begin game play and use one continue. Press Start on controller two during the countdown before using a second continue, but do not select a character. Press Start on controller one before the countdown ends. Choose characters for both players (using B on controller two to select player two) to resume game play with 99 continues.