Anyway....there were...4? Of us at first..I think....3 Cu's and a Hiyru....of course ALL of us were on Trade runs when he spawned! Thankfully I was not far from his location.
He only damages one thing at a time so you do not need to worry about matching his damage with resists. You mount to make him get off your pet. Or just toss heals on the pet. He damages tamers that are not watching him on the screen more than pets.
Mage spells and EVs damage him.
Throw down a Poison field whenever he moves around.
I use a Chiv /AI Reptalon.
I have also taken my Kirin.
His resists are so high that some pets will take a while.
We think he dies too fast on LS.
Don't run around like chickens when minions spawn
This! Invis others then yourself.
Try to keep your pets on Krampus and just move in a spiral to keep the minions in an area and invis some more.
The Hiryu is not the best choice. But I predicted there will be Hiryus.
So just to say a pet does 50 melee damage per hit.
On this Krampus a 100% energy pet would do 12.5 per hit
a Cu would do 9.75 per hit.
a hiryu 5 per hit.
Cu does less damage per hit. But we do not just have a pet with no magic. (I hope)
With the Buffs and attacks from Chiv, any pet will do higher than base damage.
Either take a pet that matches Krampus resists or take your favorite pet with a magic damage and have fun.