Here’s a thing. Last session out enchanter used a wand of polymorphing to turn a hostile ghoul into an Elf.
As a quick ruling, I ruled that “Steve the Elf” decided to join the party against the remaining ghouls and continued to accompany them until he was killed by some lizards later.
Is it really kosher to polymorph an undead creature into a living creature (provided it was a corporeal undead of course)? If so, does that then become a means of re-animating an undead comrade (at least until he hits a dispel magic)? Could one make a mindless skeleton into a trusty dwarf?
Personally, I would rule that undead and constructs are NOT subject to polymorph. If I did allow them to be polymorphed, I would let them be transformed into other nonliving materials of a similar mass. (I’ve had players in my home game polymorph doors into massive piles of cloth, for example.)
The spell description states “this spell allows the caster to change one target into another form of living creature”. While this is very clumsily written, the phrase “another form of living creature” was meant to suggest that the target has to be a living creature. Moreover, dead creatures revert to their original form.
This is explicit in Player’s Companion, which shows the point build for polymorph:
•Polymorph Other: Transform to living creature’s physical form (35), gain form’s physical characteristics (10), gain form’s physical attacks (10), and gain form’s special abilities (20) (75 total), mental characteristics replaced by new form’s (x0.2), HD limited to caster level and 2 x target’s level (x0.75), target living corporeal creature (x1), range 60’ (x1), duration indefinite (x3.5), saving throw avoids spell effect (x1), arcane (x1), total cost 39
A polymorph that is capable of affecting undead would be x1.25 more expensive.