Cheapest priced copy (Adventures in the Forgotten Realms): $0.49 at Card Kingdom, near mint, their price list as of .
Trelasarra, Moon Dancer 
Legendary Creature — Elf Cleric · 2/2 · Uncommon · Adventures in the Forgotten Realms · #346
Whenever you gain life, put a +1/+1 counter on Trelasarra and scry 1. (Look at the top card of your library. You may put that card on the bottom.)
Legal inCommanderPioneerModernLegacyVintage
Not legal inBrawlStandardPauper
2 printings · $0.49 to $2.49 at Card Kingdom
| Set | Number | Rarity | Card Kingdom | Foil |
|---|---|---|---|---|
| Adventures in the Forgotten Realms | 236 | Uncommon | $0.59 | $2.49Out of stock |
| Adventures in the Forgotten Realms | 346 | Uncommon | $0.49 | $1.99 |
3 rulings from Wizards of the Coast
- 23 July 2021Each creature with lifelink dealing combat damage causes a separate life gain event. For example, if two creatures you control with lifelink deal combat damage at the same time, a "whenever you gain life" ability will trigger twice. However, if a single creature you control with lifelink deals combat damage to multiple creatures, players, and/or planeswalkers at the same time (perhaps because it has trample or was blocked by more than one creature), the ability will trigger only once.
- 23 July 2021An ability that triggers "whenever you gain life" triggers just once for each life gain event, no matter how much life you gain.
- 23 July 2021If you gain life at the same time Trelasarra, Moon Dancer is dealt lethal damage, it dies before its triggered ability can put a +1/+1 counter on it, but you will still scry 1.