Unlock Ravage
To unlock Ravage in Arcade or Versus Mode, at the Character Select screen, stop on Cheetor, Hold the Z Button and press A. Now, Use the Left and Right to cycle through the color selections until you see Ravage.

Unlock Blackarachnia
To play as Blackarachnia, highlight Tarantulas at the character select screen and press Z and A. Then move left or right to select the new character.

Unlock Starscream
To play as Starscream, highlight Waspinator at the character select screen and hit Z and A. The move left or right to select Starscream.

Unlock Tigatron and Ravage
To play as both Ravage and Tigatron, highlight Cheetor at the character select screen and press Z and A. Then move left or right to select the other to characters.