Mutation

The Mutation is a grotesque transformation triggered by the internal conflict within Fused Zamasu's body during Dragon Ball Super's Future Trunks Saga. When his mortal half began rejecting his immortal half, the resulting instability warped his physical form into something monstrous and unpredictable. The right half of his body became a bloated, purple mass resembling corrupted flesh.

When Goku Black, a mortal body inhabited by Zamasu's soul, fused with Future Zamasu, a true immortal, through the Potara earrings, the resulting entity inherited a critical flaw. One half of his body possessed genuine immortality while the other did not. Under the immense stress of battle against Goku and Vegeta, this contradiction manifested physically as the Mutation.

Yes, the Mutation actually increased Fused Zamasu's combat power even as it destabilized him mentally. He grew taller, more aggressive, and capable of withstanding attacks that would have overwhelmed his normal fused state. The corrupted mass on his body could regenerate and even expand, giving him additional reach and striking power.

The right half of the body becomes a bloated, purple mass resembling corrupted flesh, while the right eye changes to purple with a yellow sclera. Overall height and bulk increase dramatically, and the user's aura shifts to match the dark pink energy of Super Saiyan Rose. Against Vegito Blue, Zamasu powered up further into a truly gigantic version of this form.

No, the Mutation is not a transformation that the user seeks or trains toward. It is a consequence of a fundamental contradiction within his being, occurring involuntarily when an immortal body fused with a mortal body begins to destabilize. The form is a sign of fundamental instability rather than controlled power, and the grotesque appearance reflects inner turmoil rather than mastery.