Underworld Breach

Escape was designed as a graveyard mechanic gated by resource cost: pay the printed cost, then exile three cards to buy the spell back. This staples that clause onto every nonland card in your graveyard at once, for two mana, and that reframing is the whole engine. What was meant as a one-time recursion payment becomes a self-fueling loop the moment you introduce cheap cards that refill the graveyard faster than you exile from it: a zero-cost spell that draws or mills replaces its own escape fodder, and the chain continues until you decide to stop. The end-step sacrifice is the only brake the card carries, and it is a loose one, because a combo does not need to survive to your next turn if it kills this turn. That is the tension escape's designers underrated: the mechanic assumes you are trading graveyard depth for a single valuable recast, but priced at a whole graveyard's worth of escape access, the exile cost stops being a limiter and starts being a fuel gauge. The result is one of the most scrutinized combo enablers of its era, restricted or banned across multiple formats not for a splashy standalone effect but for how quietly it turns a stocked graveyard and a couple of cantrips into an arbitrarily long turn.