Black instant 4-cost common aggro: See Challenge # 167.

Aggro is happy to have plenty of black instants, but ideally they cost 2 not 4. 4 cards are ideally finishers.

I debated something that just caused life loss in one way or another, which seemed like a good finishing card, but I couldn't find a way to justify it being instant. I wasn't sure if "each/target player loses 5 life" was ok at black, being so similar to red cards. And I debated something that could temporarily eliminate multiple blockers, but they all felt uncommon.

Hm. My first reaction is that it's a pity this is so much worse than Blood Curdle, but that was pretty pushed: normally the 4 CMC "destroy target creature" common card is either (Bake into a Pie), sorcery (Eviscerate) or both (Daring Demolition, Impale). But actually Blood Curdle really was pushed, and this is comparable to Flatten / Fatal Fumes / Strangling Spores with a more aggro slant, which is exactly what you were going for.

(Rare and uncommon of course have more of the instant Murder-with-upside: Eat to Extinction, Hour of Glory, Price of Fame, plus Silence the Believers, Hagra Mauling, Drag to the Underworld and Vraska's Contempt at 2BB.)

Thank you for finding some good comparisons, I glazed over trying to analyse what was available :) Yeah, this wasn't especially strong, but it depends very much what environment it's in.

I considered making the base effect stronger -- -4/-4 or -5/-5 would be entirely possible -- but then I thought it was more like an "every deck" card than an aggro deck card. And I considered making it -3/-3 with a different bonus, e.g. draw a card. But the only bonuses I could think of were "draw a card" which felt mildly less aggro, and "controller lose life" which felt wrong with the life loss condition already.