Cheapest priced copy (Dominaria United): $0.35 at Card Kingdom, near mint, their price list as of .
Tatyova, Steward of Tides 
Legendary Creature — Merfolk Druid · 3/3 · Uncommon · Dominaria United · #222
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.
Legal inCommanderPioneerModernLegacyVintage
Not legal inBrawlStandardPauper
3 printings · $0.35 to $0.49 at Card Kingdom
| Set | Number | Rarity | Card Kingdom | Foil |
|---|---|---|---|---|
| Dominaria United | 222 | Uncommon | $0.35 | $0.49 |
| Dominaria United | 321 | Uncommon | $0.35 | $0.49 |
| Dominaria United | 362 | Uncommon | — | $0.49 |
2 rulings from Wizards of the Coast
- 9 September 2022You may choose to target the land that entered the battlefield with Tatyova, Steward of Tides’s triggered ability.
- 9 September 2022If multiple lands enter the battlefield simultaneously, all of those lands are counted. For example, if you control six lands and two lands enter the battlefield at the same time, Tatyova’s ability will trigger twice.