Rex Mason was a security guard at Stagg Industries who was in love with Sapphire Stagg. After being trapped in a chamber and gassed with chemicals by Sapphire's angry and corrupt father Simon Stagg, Rex mutated into Metamorpho.
In "Toxic", Rex Mason wanted to marry Simon Stagg's daughter, Sapphire. On the surface Simon pretended to be happy for them but in reality he was furious and tricked Mason into getting trapped in Project Metamorpho and gassed him, mutating Rex. Rex tried to murder Stagg in anger, only to be stopped by Batman. However, Rex was assumed dead in the process. Sapphire started to blame Batman for the whole thing until Batman showed her the video of Simon's participation in the procession of Rex mutating.
In "Monsters", Rex was secretly hiding in Old Gotham to keep an eye on Sapphire. Rex helped the people of Old Gotham when armored gangsters started terrorizing the neighborhood since he couldn't stand seeing innocent people get harmed. Rex was dubbed by the media as "The Golem". When Batman and Katana arrived to investigate, they found Rex and helped him stop the armored hoods. Katana renamed Rex to Metamorpho and Batman was able to stop the attacks by blackmailing Sapphire.
In "Alone", Metamorpho was one of the people who helped Man-Bat, Oracle, Katana, Batman, and Alfred Pennyworth against Death Stroke by helping to disable the bombs set up in the bat cave. In the end, Metamorpho joined a group that was formed called the Outsiders.
- Elemental transmutation
- Shape shifting
- Superhuman Strength
- Enhanced Durability