Cost Alternative

Spells that print an explicit alternative cost, letting you cast them by paying something other than the mana cost, usually phrased as "you may pay X rather than pay this spell's mana cost." Fireblast lets you sacrifice two Mountains, Gush returns two Islands to hand, Commandeer exiles two blue cards, and Force of Negation exiles a blue card. The reward is explosive tempo, casting a heavy spell with no mana up. Overlaps heavily with Free Spell, the subset that pitches a card from hand for zero mana; this broader set also covers land-sacrifice and life-payment alternatives. Distinct from Cost Reducer and Spell Cost Reducer, which only shave generic mana off the normal cost rather than swapping in a wholly different payment.