I am on an international trip, quite complicated (any trip from Tajikistan is). Please grant a 12-hours delay, I will try to submit my turn before anyway, but I am not 100% sure I will manage.
The first time, I magic dueled it to death with a bunch of Astral-1 lizards - some luck involved.
The second time it ran into my army, and got quite a few afflictions - less tenticles was one. I had foul vapors up and a litle poison helped. I don't remember what killed him in the end but it may have been an underwater Sleeper with an Etheral Crossbow.