Alter Self allows changing into the form of any small or medium humanoid. Would this include the hybrid forms of lycanthropes, such as the wererat or werewolf?

I can't find anything that would suggest not, but it somehow seems against the intent of the spell.

Seems a perfectly reasonable use of the spell to me. I might rule that a player has to have actually seen one, or at least make a Knowledge Arcana roll to have read about them in an illustrated bestiary, but I don't see a huge problem with it.

*Checks.*

The HD limit's gone, so that's not a worry. Lycanthropes are indeed of the humanoid type, so that's not a worry. The bonuses are all standardized, so there's not a balance worry.

Nope, nothing wrong with it at all. Just mind that you stick to the small and medium werecritters; no werebear form out of Alter Self.

Providing the creature possesses the humanoid subtype. Keep in mind though that you need a piece of the creature whose form you plan to assume. Taking it from a slain one doesn't count either, lycanthropy is a curse and death lifts that curse restoring them to their human form. The piece would need to be acquired while the lycanthrope was in one of its form other than 'human'. A tooth, claw, or clump of fur.

Considering the rarity of lycanthropes this material component is worth more that the amount covered by the 'Eschew Materials' feat. A material component consists of one or more physical substances or objects that are annihilated by the spell energies in the casting process.

Personally I'd say yes to the shape, but obviously the PC would not gain any benefit of lycanthropy outside what the spell specifically states. They'd also need the appropriate feats to take full advantage of the beasts claws and fangs and they'd also need the material component.

Joys of the spell component pouch. Comes complete with ready live spiders, lycanthrope fur, illithid brains, tarrasque hearts, and relics.

Would this include the hybrid forms of lycanthropes, such as the wererat or werewolf?