Plaza of Heroes is a rare Land card from Dominaria United Promos (PDMU), collector number 252p. Current market price: $10.01 (foil $7.62), TCGplayer market prices via Scryfall.
{T}: Add {C}. {T}: Add one mana of any color. Spend this mana only to cast a legendary spell. {T}: Add one mana of any color among legendary permanents you control. {3}, {T}, Exile this land: Target legendary creature gains hexproof and indestructible until end of turn.