Magmatic Sinkhole

The printed cost is a lie you get to negotiate down. Six mana for five damage to a creature or planeswalker is a rate nobody would run, which is exactly the point: the sticker price exists to be paid with cards you were never going to cast. Delve turns a graveyard full of spent fetchlands, dead spells, and dredged-over dross into removal, and once the yard is stocked the effective cost collapses toward a single red mana. That is the trick of delve as a mechanic: it does not make the card cheaper so much as it converts a resource you already burned through into tempo, letting a graveyard-centric deck cash in its history at instant speed. Five is the number that matters, wide enough to kill the planeswalkers and midrange threats a two-damage burn spell shrugs off, and hitting at instant speed means it functions as an ambush during combat or a response on the stack rather than a scheduled sorcery. The design resolves a familiar tension for graveyard decks: they want cheap interaction but hate paying mana for it, since their mana is spoken for by the engine. This answers that by pricing itself in graveyard cards instead, a removal spell that only sharpens as the rest of the deck has already done its work.