Plunge into Darkness

The second mode is the part that broke into eternal formats, and it broke clean: pay life to dig as deep as your life total allows, then keep exactly one card and exile the rest. The exile clause is what keeps it honest as a dig rather than a tutor; you do not assemble a chain, you make a single hungry plunge and pay for it in life you may not be able to spare. That made it the engine piece for combo decks built to convert a high life total into a guaranteed answer, where the sacrifice mode and the entwine cost stop being filler. Sacrifice a board of creatures to bank life, then immediately spend that life to find the card that ends the game, all at instant speed, all on one card. Entwine ties the two halves into a single fork: it is rare for a modal instant to let one mode generate the resource the other mode consumes, and rarer still to do both in one casting. The life economy is the whole tension. You are never paying mana for the cards; you are paying with the only number that keeps you alive, and the card hands you a way to refill that number right before you burn it down. That self-contained loop, build life, spend life, dig, is why it kept surfacing in dedicated combo shells long after the rest of its era's instants faded into the binder.