Thorns with the Pale Helmet doesn't react to all attacks.

Current list of attacks it does not respond to:
Iktab, The deathlord - orb in center of arena that shoots mutliple projectiles.
Zicoatl, Warden of the Core - Any of the laser or electricity attacks do not register.
venom priestest at the base of pyramid - any attack while she is floating does not reflect damage.
blood priestest - triple blood attack
beira of the rotten pack - ice spike attacks do not atcivate thorns
brambleghast - double chaos mace type attack
Faridun Plaguebringer - none of his attacks activate thorns
Archer Transcendent - None of their attacks activate thorns or Bloodbarrier
undertaker of armageddon - no attacks activate thorns or bloodbarrier