There have been several cards in the past that produce extra mana but restrict it to 'spells/costs containing X,' but none of them have been particularly impressive
Flesh Carver is on theme for bodies and for sac outlets and while not up to the premium levels of the best in slot cards he is still perfectly serviceable on those fronts
Asmoranomardicadaistinaculdacar was particularly hard to design because its name removes the space for the mana cost, imposing an alternate cost
Restoration Seminar Restoration Seminar represents a flexible reanimation spell you get each turn and after two turns you come out way ahead on mana
At $4, this is one of my favorite spec targets in Throne of Eldraine Standard right now
(Food is an artifact with ", , Sacrifice this token: You gain 3 life." Treasure is an artifact with ", Sacrifice this token: Add one mana of any color.") Tabletop Magic Online Price History Tabletop Magic Online