Sovereign's Realm is a mythic Conspiracy card from Conspiracy: Take the Crown (CN2), collector number 10. Current market price: $0.35 (foil $11.40), TCGplayer market prices via Scryfall.
(Start the game with this conspiracy face up in the command zone.) Your starting deck can't have basic land cards and your starting hand size is five. Exile a card from your hand: This turn, you may play basic lands from outside the game. Basic lands you control have "{T}: Add one mana of any color."