
I don't find myself a fan of this card. Usually when something is dishing out a single point of damage I am looking to take out those pesky 1 cost enemies like a wil o' wisp or a cultist at a location that I can't afford to fail taking out or will slow me down. But, unlike using something like the Lantern which would remove it at any point in your turn, the Coup de Grâce requires (well not quite requires, but you won't want to do so otherwise) you to do it as your last action in the turn. I could wait until the last action to remove the wisp, but then I would be suffering the rest of the turn from stat reductions until then and if I take something out early in the turn I have lost valuable actions in doing so. Of which, I was likely better off evading and just walking away half the time.
There are circumstances that could arise, but I think this will be the card that sits in your hand waiting for those circumstances to arise that never gets played. You end up walking into a room last action and then take something out and draw a card sure, something like that or you fall short in one attempt or two and something needs a finishing blow, or your left something on one hit point left sure. I would often likely find myself holding this in hand and then just throwing it for the icons because those situations don't show up. That's what I feel like the normal use of the card would be as I play.