I get the impression this is something you're making up and not something from a book?
So the idea is you shapeshift (X/day) and when you do, you become two animals, each with their own independent actions?
It seems relatively powerful, but not game breaking. My first thoughts would be to limit perhaps that your maximum size is reduced by one when using the ability (so, currently, you'd be able to turn into two small animals, such as bob cats, or whatever). I was thinking of having the shifting take a full-round action, but unless there is a duration attached (like you can only stay shifted for one minute, or whatever), then there'd be no point to that limitation. Perhaps both forms have to stay within 120 feet of each other, or something, too.
What are your thoughts?