MonsterEnvy
Legend
So you're just going to give up and die? You won't even try to disintegrate the roof and fly away, for example? Or collapse the ceiling so he has to waste time tunneling through? Or recruit minions by regular intimidation so that the warlock becomes nothing more than a human with 14 arrows in his chest?
You give up too easily.
Or once again go for Rules as Intended and just say that if the Beholder knows that guy is hidden there. It can fire one of the Laser that come out of it's eyeballs at it.