Just posted Lothor so that he can get in the fight. He isn't charging in with his sword as he normally would. I'm betting on a blink back to Ulthok. (Look out little guy!) And at the very least he can teleport all over. So Lothor is going to use his two hand axes of throwing which should allow him to follow the thing around - especially if he guesses right on where he might move.
This thing has Blink abilities that it can control. It is sort of like the Gith things that move between plans at will.
So check all the clues, it is very quick, it can move between plans at will, it's bite and claws are not hampered by our armor. It can be hurt, but we don't know how much damage it can take. It took a direct freeze but kept moving.
The melee has had some effect, we really need to keep hurting it before it can kill us.
So back to the monster book..what the heck are we fighting?