Brago's Favor

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.) Spells with the chosen name you cast cost {1} less to cast.

From Magic: The Gathering.

Open the interactive version on https://mythscribe.cloud/app/tcg/cards/cms6ohxw3cwpppb1hycdckaee.