This event says: "Response: After you attack and destroy an enemy, shuffle the encounter discard pile into the encounter deck and discard cards from the top until an enemy is discarded. Add that enemy to the staging area to discard a non-unique location with threat equal to or less than that enemy's threat."

Seems easy enough, but then I started to wonder... if there is no location with threat equal to or less than that enemy's threat, would the enemy not go into staging? So basically, if the condition "discard a non-unique location with threat equal to or less than that enemy's threat" can't be met, then does the effect of "Add that enemy to the staging area" not occur? If so, that would seem to make card more viable, as otherwise, you could make your situation worse... which may be the risk intent, but now I'm wondering.

13 minutes ago, JYoder said:

..if the condition "discard a non-unique location with threat equal to or less than that enemy's threat" can't be met, then does the effect of "Add that enemy to the staging area" not occur?

Yes.

Adding the enemy to the staging area is considered the Cost. And an ability's cost cannot be paid if the resolution of its effect doesn't change the game state. So if there are no eligible locations in the staging area then that enemy you discarded would stay in the discard pile.