M.U.G.E.N.
It is a 7-button (A,B, C, X, Y, Z and Start) game which includes Joystick, arrow keys, letters, number keys, number lock keys and function keys (for debugging). The main mode in menu screen is Arcade Mode, where you can choose only 1 character if you want to play it and fight random characters like other fighting games, especially Team Arcade and Team Co-op modes. VS mode is a 2-player challenge where you can play against your friend. In Team Arcade and Team VS modes, you can play with 1 non-playable character to beat opponents, excluding Team Co-op and Survival Co-op modes. In Survival mode, it is the endless stream of opponents where you can fight them. In Watch mode, you can see the characters with AI during the fight but you can't play as the character unless you press function that turn into playable character if the option of debugging keys is on.