Have say a 1 in 50 chance for a dungeon to have a special glow to it. Or something very obviously identifying it being aside from the norm. When entering, it is the exact same except it has a warning mechanism telling you that your pet has no use here.
Since it makes the dungeon vastly more difficult for the majority of players and characters. It could grant a special reward at the end. Possibly a chest after the boss has died with the same exact drops, or maybe add a flair to the UTs dropped saying that it was earner in a petless dungeon.
Deca could even sell these as Petless Keys or Challenge Keys somewhere for same/more gold.
All these other than the core “Rare chance for forced petless dungeon to spawn instead of normal” are brainstorming so please address the actual idea.
Thoughts?