Zaira Zatara:
In reply to Neva Trevail (msg # 223):
When you cast this spell, you can assume the form of any Small or Medium creature of the humanoid type. If the form you assume has any of the following abilities, you gain the listed ability: darkvision 60 feet, low-light vision, scent, and swim 30 feet.
Small creature: If the form you take is that of a Small humanoid, you gain a +2 size bonus to your Dexterity.
Medium creature: If the form you take is that of a Medium humanoid, you gain a +2 size bonus to your Strength.
(nymphs have swim, I think succubi have dark vision - so do other creatures though?)
Careful with your interpretation of Humanoid there. Neither Nymphs nor Succubi are Humanoids. If you want Dark Vision, Orcs. If you want Swim, Lizardfolk. Not to rain on people's parade, but just because it has two legs, two arms, and one head does not make it a humanoid. If we're going to (ab)use the rules, stick with things on the humanoids list.