Well, almost all. It is, for instance, difficult to stun someone who's already been stunned. In fact, you might just snap them out of it.

The Revenant grunts loudly as he is jolted out of his healing-induced nap. "Well, can't say I wasn't warned," he mutters.

Bus: stopped. Occupants: dazed and experiencing muscular seizures, except for him and, yes, Moon Shadow. Voices from outside.

"Situation report?" he says brusquely. He's already moving cautiously to get a better view out the window.