Werecrocodile

I know when I first saw the Werecrocodile in all its goofy glory in the pages of Sandstorm I was all pshaw running out of ideas are we Wizards and here I was thinking Weretigers were dumb. But after some research it came to my knowledge that Werecrocodiles are a legit thing (along with Weretigers and other Were-big cats), though not in the sense that were used to here in the modern West.

We've done the Werewolf before, arguably the poster boy for all werebeasts. It's a man who under the light of the full moon becomes a wolf hybrid type thing. The moon rule is followed with all the lycanthropes (an erroneous term, since the term lycanthope can only be linguistically tied to the werewolf), regardless of whatever creature you turn into. But the moon thing is a relatively new invention. Though some werewolf legends talk about transformations under certain stages of the moon, werewolves were more often described as willingly transforming through magic, usually by wearing a pelt, part of a pelt, reciting a spell or applying a potion.

So it is with Werecrocodiles. The folkloric key to becoming a werecrocodile is usually either an incantation or the wearing of a fetish.  Finding specific stories and legends is a bit tricky. I've found a lot of sites claiming that they appear in legends of Indonesia, Thailand, Zambia, Egypt and the Bakongo people. Basically anywhere where the crocodile is an apex predator. The person would transform into a crocodile and then lurk in rivers to eat people who wronged them / sexy bathers. Cannibalism is a recurring theme across the world when it comes to werebeasts.

 There's the Thai legend of Krai Thong and Chalawan (which is also a Thai film), but I'm unclean whether Chalawan is a giant/demon who can turn into a crocodile or a demon crocodile that can take on humanoid form. In Indonesia, the magical incantation/formula to take on human form is said to be tiang maleh rupa, and those who use the spell are known by the same name. In the 88th chapter of the Egyptian Book of the Dead, there's a spell invoking Osiris to give you the form of a crocodile, though the spells of the Book of the Dead are meant to aid the dead in the trials they face in the afterlife rather than affect still corporeal mortals.

Speaking of Egyptian mythology and Osiris and turning into crocodiles, you should totally buy Pantheon by Hamish Steele. It's a comic telling the creation myth according to the Ancient Egyptians. And boy I tell you I learned something from the book. Mostly that the Greek gods aren't the only ones with weird drama.

Hengeyokai

Hengeyokai are more a varied creature type than a true race. Some animals already have inherent ties to mysticism and are used as familiars or sacrifices. These same animals can find their innate magical ability growing to the point that when they reach a certain age --usually 100 years-- the animal undergoes a sudden magical burst. It gains true sentience, becoming about as intelligent as a man, as well as shapeshifting abilities, having three main forms: an animal form, a human form, and a hybrid form which looks like the animal walking on its hind legs. In fact, hengeyokai translates to "changing monster".

While a good amount of hengeyokai can pass for ordinary animals, become slightly malformed by their transformation, usually gaining an extra tail. Even when shapeshifted, the animal's true nature may be exposed by a body part that won't transform (again, usually the tail), vaguely bestial features, or markings remeniscent of their true form. The hengeyokai may also be exposed by their appetites -- many a cat hengeyokai is exposed by being caught eating dead birds while in human form.

The hengeyokai are primarily tricksters, using their abilities to steal or cause minor inconvenience to surrounding human populations. Especially malevolent hengeyokai will take on the form of a person in a household, murder them, and take their place. Animals prone to transforming are foxes (kitsune), racoon dogs (tanuki), cats (bakeneko), badgers (mujina) and dogs (inugami).