It seems to me like 2 separate characters.
1 is a full caster in name only, but with almost no class abilities.
The other is called "Eidolon" instead of Master Of Many Forms,
and would require a solid combing through on all those abilities.
Fused is why 3e Gestalt is weaker than 2 PCs.
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I'd say run it as is, with the PC knowing the overdeity
has a few chaos and pique based nerfs on the way.
No guide as to how to play it better, with lots and lots (and lots)
of stuff going on, is tactically difficult.
Besides you could always target the party with 1 more mook.