After seeing that some spells are now available as rare drops from fights, it made me start to think of other ways that spells could be acquired.
As a pet-raiser, it occurred to me that some of the pet-specific spell cards are unique and pretty neat. I wonder whether it would be possible to have a pet-specific spell card enter into a wizard's spellbook.
The mechanic could be a function of training...upon training a pet to Epic, perhaps; or even in a future pets update allow for training beyond Epic to a Familiar status.
The mechanic could also be a Purreau-type service whereby an epic pet can be "integrated", becoming a part of the wizard (like a wizard's familiar) and the wizard could acquire spell cards, health, mana, powerpip boosts from a pet after integration. Obviously, it would be a costly service (in gold or crowns) and remove the pet from inventory.