At-will, standard action, self, concentration, DC 17+; you transform yourself into a beast. You assume the physical form, senses, and movement modes of the chosen creature, but retain your mental attributes, personality, and ability to concentrate on spells. Your equipment melds into your new form. The DC depends on the creature's size and power:
Creature Type
DC
Small or mundane (cat, hawk, rat)
17
Medium (wolf, eagle, horse)
19
Large (bear, tiger, elk)
21
Huge or exotic (elephant, giant eagle)
23
Legendary (dragon, phoenix)
25+
DC +2: you can speak in beast form (your voice sounds strange but is intelligible).
DC +4: you can transform a willing creature you touch, instead of yourself.
You cannot assume the form of a specific individual creature, only a typical specimen of a species.