First let me say that obviously there is purify+ heatwave, CoC (curse of corruption) and others which get mentioned a lot. But I never hear black blood being discussed.
Ideally you'd play it in R2 when opponent has 2 cards left and defender is already on board, a very common scenario given the consistency of NG thinning cards.
Pros
It hits through defender even if he goes double defender with letho it won't matter (letho doesn't spawn battle prep, so no boost)
Its an artifact so he can't remove/lock it since it's extremely unlikely he runs HW, though he could be double cross so if you run HW, play it earlier.
Its neutral and only 7p so it should fit in a lot of decks without too much trouble, and can even be a secondary answer to double your chances of drawing an answer in R1. Not as cheap as artifact compression, but that requires a purify and can't deal with letho onto defender.
It could be an option for decks that go tall and can't use CoC like MO relicts.
Cons
It plays for zero tempo.
It's a total brick against SK/non boost decks, so best to just mulligan it in those matchups.
He can see it coming a mile away, so if you are being bled he can just pass and save kolgrim for R3. Therefore you must win R1. Also he can still renew it, but that's no different than any other removal card, except HW.
Thoughts? Experience trying it? What have I not thought of?
Source: https://www.reddit.com/r/gwent/comments/o3kg4x/dealing_with_kolgrim_has_anyone_tried_black_blood/
