I had great luck with Unborn (122), curse then ascension as above then brought in Bone Serpent (121) Barrage, Darkness, Barrage, Nocturnal. That killed it, but I had a Blighthawk waiting in the wings for liftoff.
No Infected Squirrel here. But thanks to Fluffyrock tried Mr. Bigglesworth (2-1-1) and Son of Sethe (2-1-2). Key was timing the use of Ice Barrier after Biggie went into the undead round. Used lift on Son of Sethe's first move, then Hiss. Was a squeaker but it worked dependably.
Used Mr. Bigglesworth(1-1-1) as 2nd pet with Unborn Val'kyr.
Start the fight the same as above, then swap to your Kitty. Use Ice Tomb, then spam Pounce. If you need to block a 2nd Antenna use Ice Barrier.