This ability is written Splice onto (quality) (cost). As a player casts a spell with a given quality, he or she may reveal any number of cards in his or her hand with splice onto that quality, and pay their splice costs; each splicing card’s effects are added to those of the spell cast, while the cards spliced onto the spell are kept in the player’s hand. These effects are placed after the played spell’s effects. One card, Evermind, has no mana cost (meaning it can’t be cast normally), but it does have a splice cost. Splice appears in the Kamigawa block, where the quality was limited to Arcane.
My idea for a game around the Splice mechanic is one that also uses an old favorite idea that I never got around to implementing, a linguistic based spell system. At the beginning of the game you know one word, probably blast. Other words let you splice additional effects or modifications onto the spell. So once you learn the word “fiery” you can now do a blast of raw energy or a somewhat more efficient blast of fire. Other modifiers could include subtle, large, multi, silent, the sky is the limit.
What would you design around the idea of the splice mechanic?