Transformers: Beast Wars Transmetals

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.