Bizarro Sephiroth, aka Rebirth Sephiroth is a manifestation of negative emotions and inner conflict that harbored during his life, especially the hatred of Shinra. It represents the dark and chaotic side of his psyche, the very part of Sephiroth that is consumed by corruption and despair. This very form is also the result of his exposure to Jenova and corruption it caused within him.

It is a grotesque form of Sephiroth with multiple body parts acting independently of one another as he has no control over them whatsoever. This is constant struggle while he has fallen prey to Jenova, making him overwhelmed and desolate as he completely lost control over his body and himself.

It is also his inner struggle made visible and the fact that he cannot even control his own body in here just shows how much these emotions have over him.

And about that body on his head... Find out next time.

(Experimented with a new style and I felt bad if I added more gore in here. I'll also make his "Biblically Accurate form" one day as well)