Energy Doubler

Energy amplifiers whose generation is uncapped by their own card's actions, instead piggybacking on broad game events to flood your {E} pool. Gonti's Aether Heart yields {E}{E} whenever another artifact enters under your control, and Aetherworks Marvel yields {E} whenever a permanent you control is put into a graveyard from the battlefield, letting energy snowball alongside normal play. Narrower subset of energy.energy_producer; this carve-out covers only the high-volume amplifiers whose triggers fire off recurring permanent or artifact events rather than the card's own ETB or combat. Distinct from energy.energy_payoff, which spends {E} counters rather than generating them.