Rex, also referred to as T-Rex, is a bizarre yet hilarious dinosaur who comes from the SXR123 Universe. Rex is a recurring supporting character who shows up at the Cell Games Arena, either hanging out with Cell and Kermit or looking for a fight.

Though originally killed in 'Perfect Cell Fights Rex', Rex returns alive in 'The Perfect Thanksgiving Dinner' and is been with the gang once more. Rex has probably one of the most strangest abilities of the DevilArtemis Universe: shrinking while screaming like a little girl. Rex can also grow into a giant when he roars, but this happens rarely. His insults can also severely hurt his target, causing them to spasm and pass out. This ability was used against Cell, leaving him in the hospital for an unknown period of time. Rex also has a drifting mode when his tail is pulled.