So we are playing the Serpent's Skull Adventure Path, and our sorcerer loves this spell (he calls it "chickenformizator", more or less). We finished the last game knowing we will be facing an Intellect Devourer, and they can (physically) posess bodies.
Now, I've been reading the entry on Intellect Devourers on the Bestiary, and I can imagine it is an advanced one (we are at lv 12, nearly 13). So maybe its stat block is not really all that similar to the ones in the bestiary, but even so...
The posessed body retains everything it has, so I believe (I'm not quite sure on this) it uses its own saving throws instead of the ID.
Anyway, if the thing can posess a body, it has to be dead. Baleful Polymorph works on everything not inmunne to its effects (like an undead), so I think the spell will work with that body. I also think, after reading the Aberration entry, that the ID is also vulnerable to the spell (barring its SR), but here is my question:
If the sorcerer casts the BP spell against a host body, What the hell happens if at least the Fort save is missed? Does the body turns into a chicken, with the ID bursting from it, does the ID became forced to make a fort save to not change too, or the thing remains inside of the chicken, able to burst from it at will?