Discounted Spell

Spells whose own mana cost shrinks based on game state: 'This spell costs {1} less to cast for each creature on the battlefield' (Blasphemous Act), 'costs {X} less, where X is the total power of creatures you control' (Ghalta, Primal Hunger), or a self-discount keyword such as Affinity (Frogmite), Improvise (Kappa Cannoneer), Emerge (Elder Deep-Fiend), or Undaunted (Curtains' Call). Convoke and Delve are payment substitutions in the rules rather than cost reductions, tapping creatures or exiling graveyard cards to pay for generic mana; they are included because players treat Treasure Cruise and Chord of Calling as the canonical cheap big spells, and the deck-building question ('what gets cheap when my board or graveyard is full?') is the same. Distinct from ramp.cost_reducer and spellslinger.spell_cost_reducer, which cheapen OTHER spells you cast, and from cascade.cost_alternative and cascade.free_spell, which replace the mana cost with a different cost instead of shrinking it. Alchemy cards that perpetually grant 'This spell costs {1} less to cast' to other cards are excluded for the same reason as cost_reducer: the discount lands on another card. Co-fires with cost_reducer on Hamza, Guardian of Arashin (both arms in one text box) and with keyword_granter on Mycosynth Golem (has Affinity, grants Affinity).