This is essentially black Arcane Denial that has a reverse-kicker option to cancel the draw. Goes well with Narset / Hullbreacher / Leovold / etc. Even without them, typically you'd use your other removal early game to try and pay the full retail cost late game to cancel the draw. And at times you can't wait, sometimes you just gotta kill your opponent's turn 2 Oko.
I think this competes well with a lot of the Hero's Downfall variants in high powered environments since it's modal and versatile. My top 3 Hero's Downfall variants right now are Murderous Rider / Hero's Downfall / Bloodchief's Thirst. I can see this as a supplement or a swap for Downfall / Thirst to try it out.
While I'm very pro Arcane Denial, there's more hard black creature removal spells than there are hard blue 2-cmc counter spells, and Hero's Downfall / Vindicate variants are a lot more acceptable than Cancel variants. While I do think this card is good, I think there's less of a need for it compared to Arcane Denial due to those reasons.
This card looks good to me. This is to Hero's Downfall what Arcane Denial is to Cancel, except Downfall is actually a cubeworthy card, AND this has an option to pay 2 more to negate the drawback. Don't know if it'll make it in since black does have so many other good removal options available ...but this card looks sweet.
This is far-and-away the best Vraska's Contempt variant, and being able to cleanly remove Wurmcoil Engine, Ancient Stone Idol, Ulamog, the Ceaseless Hunger, or Blightsteel Colossus for 1B gives it an edge over all the Doom Blade and Hero's Downfall variants. Of course, if you're not playing in an environment where you're facing down monsters T2, the card loses a lot of its appeal. And not being able to get around protections (*cough* Emrakul *cough* ) keeps it from being the stone-cold nuts. That all said, I think I'd be willing to replace any of the aforementioned removal options with this card. Having an Arcane Denial mode on Feed the Serpent is just absurd.
The Exile plus 2 mana cost means that this card is quite effective against cheaty decks like reanimate or tinker. - This can take out darksteel, wormcoil, or a turn 2 Oko, making it a powerful tool in situations where you often will just lose if you don't have an answer, and situations where turn 3 might be too late.
The more I think about Baleful Mastery, the better I think it is. While I was already fairly high on this, it got much higher when I began to see this as a Path to Exile for 1B that can also hit planeswalkers with a "kicker" option to negate the drawback.