“The thing about dead people is, they’re extremely flammable. And the thing about zombies is that in essence, they are dead people.”
Bob is a wizard of limited magical skills and great theatricality. He learned when he was young that sleight-of-hand and misdirection would go a great distance when scholarly learning and magical talent failed. As such, he has dressed the role and carried on in the manner of a great magician, while much of what he does is not magic at all. On the other hand, he’s quite good at small fire spells, and, if you make sure the zombies aren’t shambling towards anything important (like the church, or a haymow), fire does a world of good against the creatures.