Blasphemy on a synthesist summoner

[Poit]

Normally, blasphemy allows a Will save to reduce the effects. It also has a separate banishment effect that can be negated by a Will save at a -4 penalty. Presumably, a synthesist summoner is subject to both of these effects, but how do the saves work?

A) The synthesist makes two Will saves - one against the regular effects and a second save (at -4) against the banishment effect.

B) The synthesist makes a single Will save at no penalty against both the regular effects and the banishment effect.

C) The synthesist makes a single Will save at -4 against both the regular effects and the banishment effect.

D) The synthesist makes a single Will save against both the regular effects and the banishment effect, but lower the save result by 4 to determine if the eidolon is banished.

Which of these is correct? Or is there a fifth option I'm missing?

[FuelDrop]

might be that the banishment effect is ignored entirely, and a single save determines effects for both of them.
EDIT: i doubt it, and wouldn't run it like that myself, but it is the fifth option for the OP.

[Interzone]

I imagine I would go with D myself...

[Chris Kenney]

It's A. The two saves are separate for normal outsiders as well - weaker ones might be killed instead of being returned to their home plane, meaning they can't return or be bound again.

[Malfus]

I'd go with A.

EDIT: corrected my answer

[Poit]

Alright, thanks!