Maybe each pet could give you a unique skill if they are your active pet. The skill could upgrade as the pet levels up or you could upgrade it by feeding it an item like the other buffs, rather than with skill points.
For example,
Slimes could give you an ability to fire a slime ball, that freezes enemies in a block of slime, like the Giga Slime does. As it upgrades, the time the freezing effect would last would increase.
Rabbies could give a type of kick with high knockback, with knockback that increases as it upgrades.
These are just two suggestions (I couldn't think of a skill for Jumpkins ). I think it'd make pets more interesting than just stat boosts.
For example,
Slimes could give you an ability to fire a slime ball, that freezes enemies in a block of slime, like the Giga Slime does. As it upgrades, the time the freezing effect would last would increase.
Rabbies could give a type of kick with high knockback, with knockback that increases as it upgrades.
These are just two suggestions (I couldn't think of a skill for Jumpkins ). I think it'd make pets more interesting than just stat boosts.