Gumball Guardian Mutant is a mutated version of one of the Gumball Guardians. He was mutated by the Cake People Mutant while trying to pin it down. Flame Princess and Lady Rainicorn can be seen trying to stop him, but to no avail. Like the Cake People Mutant, he has a weakness to music. Also like the Cake People Mutant, he died after Betty Grof was fused with GOLB.
The Gumball Guardian Mutant maintains the bodily structure of the Gumball Guardian he was made from, except his appearance is now altered. He has a rib-cage for a body and his head now appears to no longer be see-through. He has glowing pink eyes and frosting on his head. Like the Cake People Mutant, his body is covered in the faces of all those who fused to make it, writhing in pain, and smoke stacks on his back emitting a black fog.
The Banana Guards attempted to save the princess from the now giant monster that stood before them. This shows to be a foolish move as once they got close enough to the hand on the monster, they fused (or assimilated) with it.
Once the Banana Guards fused with the beast, Princess Bubblegum attempted to stop it by using her jellybean-Elemental Powers. It responded by turning its head and having a swarm of Red-Eyed Owls fly out of his mouth.
Yet another similarity with the Cake People Mutant, the Gumball Guardian Mutant seems to be immune to flames. As another attempt to stop the monsters, Flame Princess tried using her fire powers to incinerate the monster’s face. She called for backup upon noticing that it was leaving no damage and was nothing more then a minor annoyance.
- Being the product of the Cake People Mutant, both mutants share many similar traits, such as their other heads seeming to not be in control and having the status of all those who combined into the creature being unknown. Another similarity includes the heads appearing to try and help sing along to try and stop GOLB.