i think it would be cool if when our pets levelled thy grew in size. This is a thing in pirate101 at it works really well. Now let me cut to the chase.
When a pet grows past ultra (Supperior) it has the ability to learn one of to specs. 1) Riding if your pet learns this you can ride on your pet like a mount. This is exclusive to large pets (Buddy dragon, minatour, vampire...) small and medium pets learn a new skill called battle Malace. This allows you to summon the pet into combat as a controllable minion.
The minions cost 4 pips 1 shadow pip to use. They would be rank 18 elite with shadow spells( since pet is linked to your soul he can also be corrupted by the shadow through you). The pet would have pet exclusive cards that would be shadow enchanted. This is so for all pets other then shadow pets (if they make them). Shadow pets would be pets of Lulu, glow bugs, mystic collosuz... they would have pure shadow hits.
Some cards I think pets could have:
(Type) shield: places a Aura on player catching 10% of damage for 40 rounds.
Some of the cards from polymorphism that no one uses anymore.
I had posted THIS idea previously, as an idea how to change things up on pets, and your idea is similar. I think pets need to be jazzed up a bit graphically, but it doesnt need to be for every new pet that comes out from here on out.