Contamination

A prison deck that wins by making everyone else’s mana the wrong color. Contamination is a {2}{B} enchantment with two clauses: at the beginning of your upkeep you sacrifice it unless you sacrifice a creature, and while it’s out, any land tapped for mana produces {B} instead of any other type and amount. Read that second half carefully — Ancient Tomb and City of Traitors produce a single {B}, not two, and a five-color mana base produces nothing but black.

You’re the only deck in the room that wanted black mana anyway. The whole problem is the upkeep cost, and Nether Spirit solves it permanently. It’s a {1}{B} 2/2 that returns itself to the battlefield at the beginning of your upkeep as long as it’s the only creature card in your graveyard. Both triggers happen in your upkeep and you control both, so you order them: return the Spirit first, then sacrifice it to Contamination. The lock costs you nothing, forever.

Zombie Infestation is the backup fuel. {1}{B} for an enchantment that turns two cards from your hand into a 2/2 Zombie token at instant speed, which converts the extra lands you draw into upkeep payments. Cabal Therapy’s flashback cost is sacrificing a creature, so spare Zombies also strip their hand.

Duress, Cabal Therapy and Innocent Blood cover the early turns before the lock is assembled. Innocent Blood ({B}, each player sacrifices a creature of their choice) is nearly one-sided here, since your creature comes back next upkeep.

The green splash exists because of Pernicious Deed, and Chromatic Sphere is what makes it castable. Sphere is an artifact, not a land — it sacrifices for one mana of any color and draws a card, so it produces green straight through your own Contamination. Deed then sweeps: {X} and sacrifice it destroys every artifact, creature and enchantment with mana value X or less. Be careful with the number: Contamination itself is mana value 3 and Nether Spirit is 3, so X=2 is usually where you want to stop.

Wasteland and Rishadan Port stack on top of the lock, and Mishra’s Factory is the clock — you don’t tap it for mana, you pay {1} to make it a 2/2 and attack. It takes a while, but the opponent isn’t casting anything.

The deck loses to enchantment removal and to speed. Naturalize and Tranquil Domain untangle the lock, Enchantress out-values it, and a draw without an early Contamination is just a slow mono-black deck. Sideboards bring Engineered Plague for the tribal decks and Dystopia against green and white.