Dont know if its a bug but Thoughtwoven Spirits gets insta killed by anything that switches ATK and DEF (Transformation Potion,Spiritbender for example)
Hailstorms, Shrivel or Hunters net own him.
If he plays weak ATK monsters, weaken them, strong monsters get pacified.
Play flying cards against pacified ground monsters (hunters net helps)
You can play weak monsters and use Relocate (gives the enemy the monster).
He can’t kill his own creatures.
Use healing! Angels tear are damn awesome to deal with his initial burst damage.
Runeword Immortal helps alot too.
Use explosive gnomes! 3 Volatile Damage owns most of his cards.
Won in 4. Game with Ravinova, had two hailstorms on my starting hand = all his 3 Monsters (the two epics + thoughtwoven spirit) were down in the first round.
Didnt have any AA-Cannon, just outdamaged him.
Wilrius with Charge potions and Siphon should work great, just weaken the monsters and mill.
Either you die very fast or you win.
But its the last stage in the current campaign, so what did you expect? Get a perfect deck for this boss!