Making a parody makes such stories fair game. This, of course, assumes that what you are going to do is a parody of the story and characters, and isn't just simply using the characters to make a whole new game. For that it would be a lot easier and less risky if you made your own characters. Teddy bears are pretty easy to model anyway, and considering the amount of different kinds there currently are, there should be no legal issue in making a game about an evil teddy bear violently murdering his friends... Unless you are planning to upload it to AG, then it might not go through.
