Killer Instinct

Turbo mode:
Note: This can be done in single player and two player mode. Select a fighter, then hold Right on joystick one and two and press Quick Punch + Middle Punch + Fierce Punch. Hold those buttons until the pre-fight match screen is displayed. Release the buttons after the second "swoosh" sound. Note: The faster speed is only effective for one match.

Fight as Eyedol:
Select Riptor as a character, then hold Left and press Quick Punch + Quick Kick. When the versus screen appears, quickly hold Right and press Medium Punch + Fierce Punch + Fierce Kick. The name "Eyedol" will be spoken to confirm correct code entry.

Small players:
Note: This requires ROM versions 1.4 and earlier. Select a stage with a platform and select Fulgore as a character. Push your opponent to the edge of the platform, execute a combo, and end it with the teleport (Back, Down, Down/Back + Fierce Kick). Press Start to reduce your opponent's size.

Random fighter:
Hold Up and press Start at the character selection screen.

Alternate costumes:
Highlight a fighter, then press Up or Down at the character selection screen.
Information in this section was contributed by ktu95a2391.

Hint: Combo Breaker after they hit the ground:
With TJ Combo, use the Roll move (press Back briefly, then Forward and Medium Punch) making sure to hold Forward after the move. Then press Back and Medium Kick after the first punch makes contact. If done correctly, it will be two. After the second hit, before your opponent hits the ground, do a juggle by pressing Back, Forward, Fierce Punch for a three hit combo. Sometimes your opponent will do a Combo Breaker after they get up. This works best under the harder difficulty settings, when you press Down and Start to get easy breakers turned on.
Information in this section was contributed by The Greg.