All Changelings have a Human form and at least one animal form. However, there are many Changelings who adopt a 3rd or even 4th form, usually of the same region as the main animal. There are many different animals a Changeling can come from, but their animals will always come from their home region.
Now, while there can be up to 3 animal forms, the more "large" animals there are, the more difficult it is to stay sane. Most changelings have a large animal at least, but they also can have an agile form, stealth form, or even a flying form.