Tell him we are just practicing for when we get back to the material plane, and we have no wish or desire to fight him.
Roll the blood minion tiger on it's back like a playful kitten... Regardless of what will happen to the rider.

I want to name the minion John.

You shout, "Please don't kill John. He didn't mean to startle you!"

Mathias says, with sword raised, "I am tasked with killing all who exist in this plane. I will even have to kill oneself... eventually."

You reply, "Then we have plenty of time. Lets all just calm down. What do you like to do for fun around here?"

"Fun? What is this 'fun' of which one speaks?" Mathias says.