The Crimson Cloak was the transformation/disguise of Clayface.
He had a skull-like face with long, grey sharp teeth and dark red angry eyes. He wore a torn apart, red cloak with red smoke covering his lower body. His hands are really embedded into his sleeve like mists. The red mist that surrounded him was slightly darker in color than him. His body resembled large ghost garments, while it was really just clay.
He was a ruthless ghost who wanted revenge and vengeance. He seemed to have a completely untameable spirit, telling Batman that it's all his fault without even telling him who he really is in the first place, and his thirst for revenge was so high, that even Batman himself could fear him, seeing him in his dreams.
Scooby-Doo! & Batman: The Brave and the Bold
When an alarm sounds from Gotham Chemical Storage, the assembled Mystery Analysts head for the warehouse, where they find that several phials with a radioactive isotope have been stolen. A red-cloaked figure from the old theater appears before them, calling himself Crimson Cloak and swearing revenge on Batman and Gotham for making him into a ghost. Crimson Cloak sets the storage on fire, but the Analysts escape the blast with Plastic Man's help.
While the superheroes put out the fire, Batman sends Mystery Inc. to a diner to rejoin them later. Following the gang's questions, he reveals the tale about his single unsolved case. Many years ago, at the start of his crime-fighting career, Batman attempted to stop Professor Milo from completing an experiment with faulty teleport technology. However, the vortex created by the device killed one of Milo's assistants, Leo Scarlett, a failure that has haunted Batman since that time. They conclude that the likely suspects behind the Crimson Cloak would be either Sam Scarlett, Leo's father, or Riddler.
Batman and Mystery Inc. visit the Riddler at Arkham Asylum. Batman, Fred, Daphne and Velma re-encounter Crimson Cloak, who releases the other inmates from their cells. The investigators just barely manage to escape their clutches and seal them inside the asylum. As they return to the Mystery Machine, they are intercepted by Harvey and the other Mystery Analysts (sans Aquaman), who attempt to arrest them for the isotope theft due to fake evidence planted in the van. Batman and Mystery Inc. make a run for it.
Shaking off their law-enforcing pursuers, Batman takes the gang to the Batcave and leaves them there to return to Milo's old laboratory for clues. Rejoined by Aquaman and Question, who refuse to believe the false accusations made against Mystery Inc., Batman finds Milo's teleporter restored by Crimson Cloak, who promptly attacks and incapacitates the heroes. Later, Batman awakes to see himself, alongside Aquaman, tied above the teleporting machine.
At the same time, when Velma attempts to analyze the footprint in the clay, the clay suddenly comes to life and attacks. After overcoming it with a Bat-Dehydrator, Mystery Inc. deduces the villain's true identity for themselves: Clayface. They try to inform Batman, but learn that he has been captured by the Cloak; and after equipping themselves with the old costumes and gadgets of Batman's former sidekicks, they arrive just in time to stop the teleporter and incapacitate Clayface with the Dehydrator. Defeated and exposed, Clayface admits that he restored the machine for the Riddler and stole the isotopes to power it, in return for a cure against the gradual decay of his body. The Riddler sitting in Arkham is revealed to be a clay decoy, and the Question is unmasked as the real Riddler, who had taken Question's place during the fight before the Analysts' meeting.
- He is similar to the Red Ghost.