Each sprite pack should come with a license (like the fair use CC they use in the AP: give credit and it's OK), if it's officially released. If you're using ripped sprites it's a different story, but there are plenty of such sprite animations floating around that copyright holders don't find or mind. Usually the original authors don't care, but if you want to be certain, asking for permission is the only way.
Greasegoat
I don't think you will get in trouble but I don't really know.