Avengers Tower

{T}: Add {C}. {T}: Add one mana of any color. Spend this mana only to cast a Hero spell or to activate an ability of a Hero source. {4}, {T}: Look at the top three cards of your library. You may reveal a Hero card from among them and put it into your hand. Put the rest on the bottom of your library in any order.

From Magic: The Gathering.

Open the interactive version on https://mythscribe.cloud/app/tcg/cards/cms6o49561wsjpb1hfaug8dr2.