If this spell looks decent to my GM and reasonably interesting, I have an NPC ranger that is likely to research it ('s right, ranger spell research!). The main question is whether it ought to be Rgr 2 or Rgr 3, and probably Drd 2 either way. Comments are invited. For comparison, there is a Drd 4/Rgr 4 spell in the Spell Compendium called wild runner which changes the caster physically into a centaur (Str/Dex/Con mods, physical form, land speed, darkvision, no mental change). For a humanoid, it also seems like the two classes getting one limited facet of alter self.
Most spells are pretty humanoid-centric, for the obvious non-objectionable reason that that's what most people play. The purpose of this spell is primarily for centaurs, bariaurs, and other monstrous humanoids to take on a convenient bipedal shape; elves are chosen because of their traditional connection to nature, since a centaur is more likely to be a druid or ranger than a sorceror or wizard (who get alter self and polymorph, though interestingly, alter self also won't let a centaur (monstrous humanoid) change into an elf (humanoid)!).
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Elf Form
Transmutation
Level: Drd 2, Rgr 2
Components: V, S, DF
Casting Time: 1 standard action
Range: Personal
Target: You
Duration: 10 min./level
In order to cast this spell, you must be a Small, Medium, or Large aberration, dragon, fey, giant, humanoid, or monstrous humanoid.
Your shape changes into that of an elf of the same age class and gender as yourself (choosing deliberately if you do not natively have a gender). You can specify minor physical details such as hair color and height, within racial norms. You gain +2 to Dexterity and -2 to Constitution for the duration, lowering your maximum hit points by 1 hit point per HD, possibly reducing your actual hit points (which are not restored at the end of the spell). Your base land speed is 30 feet.
You gain low-light vision and a +2 on Listen, Search, and Spot checks. You gain a +10 to Disguise checks and Use Magic Device checks to pass as an elf, including as a specific elf; spells and spell-like abilities treat you as an elf unless the caster passes a Spellcraft check with the DC of 12 + your Wisdom bonus.
I think that's a spell that I would never pick as a PC, when I could just use Alter Self and get some of those special abilities.
Though the monstrous humanoid restriction is lame and something I would drop right away as a DM, I'm sure that there are ways around it such as disguising yourself as another sort of monstrous humanoid that has an elf form.