Cerberus is a hellcat or grim cat as he's described in the show and Macey's pet. He has black fur, yellow scleras, and fiery orange irises.
Cerberus is shown to be either naturally aggressive, mischievous, or friendly, depending on what is going on.
He has the power to shoot a fiery lava substance from his mouth.
Trivia:
Cerberus is named after Macey's favorite mythical creature.
It's possible Cerberus is the only hellcat in universe.