Vs. Duel mode
While starting the game with two players, stay close enough so no enemies appear. Then, have both players attack each other.
Hints
Defeating Abobo
While fighting Abobo at the end of mission 1, keep kicking him while he is not moving. However beware of his throw and double punch clap smack.
Defeating Jeff
While fighting JeJeff at the end of mission 2, keep kicking and punching him until he is defeated.
Defeating Big Boss Willy
While fighting the last boss Willy at the end of mission 4, have player two attack his men and distract him. Then, have player one punch him directly in the head. While player one is being attacked, have player two punch him again. While player two is being attacked, have player one kick him. Repeat this until Willy is defeated. Note: Watch out for his gun.