If there were an infinite number of universes will it be true to say that every conceivable (imagination) life form exists somewhere? Example, somewhere in a universe a 3 headed dragon exists - or does mathematical limit apply in this case?
This isn't a physical question. Physics is about getting results from some principles. Here we have no principles to start with! The answer can be anything you want.
Also your question is related to biology too. Is it actually possible to have dragons? What is the origin of life?
I think this is one of those questions I can simply call a wrong question.
Mathematics is not physics. Whatever creatures exist in these universes they would still need to follow the laws of nature in that universe. Since we don't know what laws other universes would follow, so there's no way to answer your question. Now, since this topic isn't mainstream science, thread locked.