If youve ever read the golden compass, there is a pet like thing in there (more like a companion in animal form) and its linked to u and such and it can transform!! But once u grow older (maybe in graal once u get stronger) it loses its ability to trans-form. I think that would be pretty neat....if there was a pet like that, but u would be born with the pet not find it in the wild. Oh and also in the book it fights but there are some rules with it.
And its called a Daemon.
1. Other people cant touch it.
2. People cant harm it only other daemons can.
3. If you seperate it hurts!
4. When it gets hurt, you get hurt and vise versa.
It might to some hard scripts! But i think it would be so cool!!!