Is Merged Zamasu getting weaker?

[WhatsUpPigeons]

Zamasu might have an internal breakdown after seeing his face "What?? A god like me look like this?" turning him insane.

[Saturnine]

I think it might have been caused by one of Vegetto's ki attacks - it was so overwhelmingly more powerful than him that it completely obliterated the right side of his body, and it's simply taking that long to regenerate. Kinda like how Buu's regeneration begins to fail him once he's been beaten hard enough.

[Shinomori]

Zamasu's body is caving in on itself.

This could be because...
a) Like you mentioned, they fused while Goku Black was a SSJR. The writers would need attention to detail for this to be the case though.
b) Zamasu fused with a body that had a soul that didn't belong to it.
c) The same people fused with each other, creating a horrible instability, as they shouldn't exist in the same timeline together.
d) He's just too strong. Immortality + ever increasing power might be too much for one body to handle.
e) I'm wrong and Vegito (or someone else) basically kicks the immortality out of Zamasu, forcing him to start melting. This fits Super's logic the most.

I predict it will be (d). Since Black wasn't immortal, that half of him can't handle the immortality along with the ever increasing power aspect. I think this may be the first villain in Dragon Ball, that pretty much defeats himself. I know Frieza technically lost because he couldn't control his power twice, but in this instance Merged Zamasu will explode because of his power. With Frieza, his power decreased over time, allowing Goku and Vegeta to become stronger and take him out.

[YonedgeHP]

The mutation can be caused by the time ring, for making a malicious use of it as both can't exist in the same timeline, breaking the taboo of a god, which causes instability in his body. This matches perfectly with certain ancient cultures where a deformed body was considered a divine punishment.

PD: Curiously enough, the damaged arm is the same where he keeps his time ring.

[MadSaiyantist]

It could be Merged Zamasu getting split between Zamasu and Black's signature abilities: Immortality and Power Adaptability. His body can't decide whether to feel the pain and use it to get stronger or to completely ignore it.

[marcbret87]

Merged Zamasu looks in the NEP is like Two-Face. I am guessing that Merged Zamasu is not fully inmortal, and hence one half of it's body is indeed getting damaged while the other is not.

Seems like I had it half-right

[Potanical Pardon]

The Two Face symbolism is cool, but he should still be immortal, just not heal.

I would've loved to see a fully damaged, crushed and crippled Zamasu in absolute pain, but just not be able to die to have the pain finally end. Maybe not even be able to communicate, speak, breathe, and think. Too dark? Nah, we've seen Krillin get exploded and repeatedly impaled a bajillion times.