Cloud of Darkness
Golgari's graveyard payoffs usually count creatures, or count lands, or count both and call it a day. This one counts every permanent card in the yard and pays it straight into a scaling -X/-X, which quietly changes what a self-mill or sacrifice engine is building toward. Fetchlands, cracked mana rocks, dead creatures, spent enchantments: all of it is ammunition, so the removal it delivers on arrival is only as small as your first few turns and only as large as your graveyard has grown. What complicates the math is that the enters trigger fires exactly once, on a five-mana body, so the card asks you to time it for maximum yard rather than jam it early. Land it off an empty graveyard and X is zero, so the target gets -0/-0 and nothing happens at all; land it in a grindy midgame after a dozen permanents have died and it erases almost anything, or shrinks a blocker to nothing and opens a lane for the flier the following turn. That flying matters more than the modest 3/3 body suggests, because it turns a removal spell stapled to a creature into a clock the opponent has to answer twice. What keeps the effect from being a hard sweeper is its single target and its once-only window: it punishes a full graveyard, but it cannot punish a full board.
