Cheapest priced copy (Throne of Eldraine): $0.49 at Card Kingdom, near mint, their price list as of .
Lochmere Serpent 
Creature — Serpent · 7/7 · Rare · Throne of Eldraine · #381
Flash
{U}, Sacrifice an Island: This creature can't be blocked this turn.
{B}, Sacrifice a Swamp: You gain 1 life and draw a card.
{U}{B}: Exile five target cards from an opponent's graveyard. Return this card from your graveyard to your hand. Activate only as a sorcery.
Legal inCommanderPioneerModernLegacyVintage
Not legal inBrawlStandardPauper
4 printings · $0.49 to $1.49 at Card Kingdom
| Set | Number | Rarity | Card Kingdom | Foil |
|---|---|---|---|---|
| Throne of Eldraine | 195 | Rare | $0.49 | $0.49 |
| Throne of Eldraine | 381 | Rare | $1.49 | $0.99 |
| Throne of Eldraine Promos | 195p | Rare | $0.49 | $0.49 |
| Throne of Eldraine Promos | 195s | Rare | — | $0.49 |
5 rulings from Wizards of the Coast
- 4 October 2019You can't activate Lochmere Serpent's last ability without targeting five cards in a single opponent's graveyard.
- 4 October 2019An Island is a land with the subtype Island, not any land that could produce blue mana. For example, Mystic Sanctuary is an Island, but Castle Vantress isn't. Similarly, a Swamp is a land with the subtype Swamp, not any land that could produce black mana.
- 4 October 2019If up to four of the target cards are illegal targets by the time Lochmere Serpent's last ability resolves, the remaining legal targets are exiled and Lochmere Serpent is returned to your hand.
- 4 October 2019If each target card is an illegal target by the time Lochmere Serpent's last ability resolves, the entire ability won't resolve. Lochmere Serpent won't be returned.
- 4 October 2019Activating Lochmere Serpent's first activated ability after it has become blocked won't cause it to become unblocked.