Tendrils of Corruption

The damage scales with your Swamps, which makes this a removal spell that gets better the more committed you are to a single color. That commitment is the whole bargain: in a deck splashing black it kills almost nothing, but in straight mono-black it routinely deals six, seven, eight to a creature while swinging the life total by the same amount. The lifegain is the second job stapled onto the first: like Corrupt and Consume Spirit, this one counts Swamps twice, once to kill and once to climb out of range. Instant speed lets you hold it through combat, stabilize against an attacking board, and answer a threat at the same moment you recover the life. It belongs to a long line of black removal that asks you to pay for power with deckbuilding discipline rather than mana: the cost is fixed at four, but the effect is rationed by how clean your manabase is. That trade rewards the kind of grindy, basic-heavy mono-black build that wants to trade one-for-one all game and slowly bury an aggressive opponent under recurring life swings. Against decks light on creatures it is a dead card, and against fast starts the four-mana floor can arrive a turn too late, but as a reward for committing fully to one color it does two jobs at once that most removal splits across two cards.