It wasn't quite that cool.
We did play out the combat at the table, but I had warned all the other players ahead of time that it was fake. I trusted them to keep the secret, and play it straight. They did a great job.
But Piratecat, playing Dranko, thought it was real. He thought he was really killing the other PC's. He was pretty... vocal... about it when he learned the truth.
Ah, that's cool enough. Did you also make Piratecat do all the rolls and "decide" what he was going to cast and who he was going to spike each round? Or did you just take control of the Becoming Dranko yourself?
(What's the pluperfect of "Become"? Becombed?)