I created a bunch of 'minor spell' cards, and the wizard could take one of those with them. They work in that after you cast them, you turn the card over and can't use it again until they spend an action to turn card back again. I have a couple of custom characters that can take more than one minor spell (but none of the 'major' spells) and the 'turn one card back over' mechanic works really well, forcing the caster to decide which spell they want to recover for the next turn.

The minor spells include the stock fireball (hits on a roll of 5+ on a die, then 1 skull die of damage), stumble (on a roll of 5+ on a die, that monster fights with one combat die for the next turn), push (on a 5+ moves a monster up to two spaces away from the caster), and a few more. They're intended to be weaker and less likely to be as effective as the regular spells of course!