I would love the idea of pet parents making a new spell entirely, if you breed a pet with another pet depending on who you breed it with they have a chance to form a spell which both will have to use. Keeping these strictly pve and not OP would be the ideal place for them. This would give mastery amulets more use and people who really enjoy using two different schools to play a chance to combine the spirits/elements for a card they can then use in battle.
I will let wizard101 sort out how this would work. I am just setting the idea into motion to give the ability for it to be brainstormed.