Cheapest priced copy (Bloomburrow): $0.35 at Card Kingdom, near mint, their price list as of .
Starseer Mentor 
Creature — Bat Warlock · 3/5 · Uncommon · Bloomburrow · #233
Flying, vigilance
At the beginning of your end step, if you gained or lost life this turn, target opponent loses 3 life unless they sacrifice a nonland permanent of their choice or discard a card.
Legal inCommanderBrawlStandardPioneerModernLegacyVintage
Not legal inPauper
1 printing · $0.35 to $0.49 at Card Kingdom
| Set | Number | Rarity | Card Kingdom | Foil |
|---|---|---|---|---|
| Bloomburrow | 233 | Uncommon | $0.35 | $0.49 |
2 rulings from Wizards of the Coast
- 26 July 2024While resolving Starseer Mentor’s last ability, the target opponent chooses a card to be discarded without revealing it, chooses a nonland permanent to be sacrificed, or chooses to do neither. Then that player discards that card, sacrifices that permanent, or loses 3 life. That player can always choose to lose 3 life, even if they have cards to discard or nonland permanents to sacrifice.
- 26 July 2024Starseer Mentor’s ability cares whether you gained or lost life this turn, not how your life total changed. For example, if you gained 2 life and lost 2 life in the same turn, you still gained and lost life that turn, even though your life total is the same as it was at the start of the turn.