Hemlock Vial

A two-mana cantrip that replaces itself is cheap enough to slot into almost any black deck, so the interesting decision is what happens after it has drawn its card. Instead of sitting dead on the battlefield, it converts into a combat wrench: sacrifice it, and every equipped creature and every Equipment you control gains deathtouch for the turn. That second clause is the whole reason the card lives in an Equipment shell, since without attached creatures the ability grants deathtouch only to your Equipment. Deathtouch on your attackers turns each point of damage into lethal, so a trampling threat needs to assign only one to a blocker before spilling the rest through, and a first-striker kills its blocker before it can swing back. The grant to the Equipment itself is a narrower rider: it matters only for the handful of pieces that deal damage on their own, whose activated pings now finish anything they touch. The tension is timing versus tempo. The ability carries no speed restriction, so it can be held back and fired after blockers are declared, ambushing an unfavorable trade or punishing a defender who committed to eating a big hit. But it is a one-shot, gated behind a mana cost plus the tap, and the artifact leaves play as it activates. The life loss is the tax on the cantrip half; the sacrifice is the payoff you hold back for the swing that ends the game. It wants an Equipment deck already committed to attacking, and pays that commitment off in a single decisive combat.