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.

Summon a pair of kludujalambuses* and teach Mathias to play traditional kludujalambus duets with us!
*A mid-sized hand-held stringed instrument with a wooden neck connecting to a metal body. The string is tied from the top of the neck down over the body and the musician picks the string with a wooden plectrum. The instrument has a one octave range going from a middle to a mid-high pitch. The instrument has a quavering harsh nasal buzzy timbre.
"Fun? What is this 'fun' of which one speaks?" Mathias says.
F is for friends who do stuff together: U is for you and me... Try it! Mathias: N is for anywhere and anytime at all: Down here in the deep blue blood sea!
...Play this. On the kludujalambuses.

You have never actually played the kludujalambuses before but you bet you can figure it out as you go.

You sing, "F is for friends who do stuff together." You try and guess where to press on the cursed fabric string. There are no frets so you are more than a little off. "U is for you and me. N is for anywhere and anytime at all, here in the big blood sea. Now you try Mathias"

Mathias sings, "F is for f- friends..." he stops singing as he flubs some notes on the kludujalambuse. "I don't think I can do this."

"Don't worry Mathias. You will get better and we have plenty of time to practice."