I'm bordering on House Rules here, but it's because I want the spell to remain useful even in my reduced-racial-palette setting. This is to remain true to the spirit of the spell, while re-interpreting some of the letter of the spell.
I interpret the spell to allow you to do either or both of the following:
1) Gain specific physical appearence for the purpose of disguise. Works as stated in the rules.
2) Gain gross physical features, such as gills, scales, claw/bite attacks or wings. You may gain one of the following benefits:
- Winged flight (30 ft., Poor).
- Climb speed (1/2 land speed).
- Water breathing + "fins" (+8 on Swim checks, may always take 10).
- Claws and/or bite appropriate for size (1d4/1d6 for Medium, 1d3/1d4 for Small).
- Scales or tough hide (+3 Natural Armor bonus, maximum scales like Barkskin).
-- N