Dread0  
click place the selected card
14 play   Space spring   P pause   F fast   R new floor
Tap a card and it deploys itself somewhere dark. It comes out alive and starts stalking them, holding just past their torchlight. It will never attack on its own.
Spring is the order. Everything you have out there charges at once and fights to the death. Give it while they are still walking in and they arrive in ones and twos — and if the party's eyes sweep over one first, it breaks and goes in alone.