Opal Palace is a common Land card from Modern Horizons 3 Commander (M3C), collector number 361. Current market price: $0.27, TCGplayer market prices via Scryfall.
{T}: Add {C}. {1}, {T}: Add one mana of any color in your commander's color identity. If you spend this mana to cast your commander, it enters with a number of additional +1/+1 counters on it equal to the number of times it's been cast from the command zone this game.