This one is a bit tongue-in-cheek. I was battling solo through DW5 - Foundations of Stone (in Nightmare), and encountered a Nameless Thing (" Forced: After Nameless Thing engages a player, attach the top 2 cards of that player's deck to it...")
I was a bit slow on the uptake, so was about to defend its attack when I realised I had attached two 0-cost cards to it, so it had 0 hit points.
However, there was a Nest of Horrors staged, which had gained " Forced: When one or more cards are attached to a Nameless enemy from the top of a player's deck, attach an additional card...". I duly added a third card, which as luck would have it, was also 0-cost.
But thinking about it afterwards, did I actually need to observe the Nest's Forced effect, or would NT be dead before the effect kicked in?
And to really push my luck - would it be dead after the first card?