Tatyova, Steward of Tides is a uncommon Legendary Creature — Merfolk Druid card from Dominaria United (DMU), collector number 321. Current market price: $0.17 (foil $0.27), TCGplayer market prices via Scryfall.
Land creatures you control have flying. Whenever a land you control enters, if you control seven or more lands, up to one target land you control becomes a 3/3 Elemental creature with haste. It's still a land.