Boros Keyrune is a uncommon Artifact card from GRN Guild Kit (GK1), collector number 96. Current market price: $0.27, TCGplayer market prices via Scryfall.
{T}: Add {R} or {W}. {R}{W}: This artifact becomes a 1/1 red and white Soldier artifact creature with double strike until end of turn. (It deals both first-strike and regular combat damage.)