[Amahain]

I vote for the Chang. I remember starting a story based on that idea years ago (though mine was based on a similar Indian legend), but I never saw it through to the end.

Some other ideas to consider:

Were-hyena (aka. bultungin of bouda: Plenty of stories about these throughout Africa. Generally, it's a hereditary condition. Naturally, a lot of the stories revolve around were-hyenas digging up graves or roaming around battlefields, looking for dead people to eat.

Were-lions: Also common wherever there are lions in Africa. It's also a hereditary thing, though unlike the were-hyenas, they're a lot more noble.

Were-bear: I'm sure most of us are kind of aware of the old Norse berserkers. Shapeshifting was considered to be one of their abilities (not just into bears, mind you, but the word translates into "bear shirt", so that seems like the most appropriate animal for a story centering around that idea).

Were-jaguar: Basically, the Aztec version of the berserker.

I think it's safe to say that, wherever large predators exist, there's usually some sort of shapeshifting legend associated with them