D&Dtools

As polymorph self (see polymorph self, page 239 of the Player's Handbook), except as noted above and as follows.
You may take the form of any fiendish creature, demon, or devil that can be summoned by summon monster I-VI.
You cannot assume multiple forms with each use of the spell, but you gain all the creature's extraordinary, spell-like, and supernatural abilities.
Your type changes to outsider, and spells and effects that harm or ward evil outsiders affect you.
A spell that would banish you to your home plane ends this spell and leaves you staggered for 1 round per caster level, but does not send you to another plane.
Material Component: A bone from any fiendish creature, half-fiendish creature, demon, or devil.