What I have been thinking for LJ BST is give it a psuedo reputation bar for every genus. You gain "rep" by fighting alongside or raising a member of that family. The higher the relationship, the stronger the pet. Maybe even an ultimate version.

For example: crabs are tanky wavekin. Get it to max rep with that genus and you get access to, I don't know, Courier Carrie that has not only a unique look, but also moveset.