Secrets of Paradise

Hidden agenda (Start the game with this conspiracy face down in the command zone and secretly choose a card name. You may turn this conspiracy face up any time and reveal that name.) Creatures you control with the chosen name have "{T}: Add one mana of any color."

From Magic: The Gathering.

Open the interactive version on https://mythscribe.cloud/app/tcg/cards/cms6o4k2425kppb1hu7ydkkpo.