Cheapest priced copy (Dominaria Remastered): $0.35 at Card Kingdom, near mint, their price list as of .
Vigilant Sentry 
Creature — Human Nomad · 2/2 · Common · Judgment · #33
Threshold — As long as there are seven or more cards in your graveyard, this creature gets +1/+1 and has "{T}: Target attacking or blocking creature gets +3/+3 until end of turn."
Legal inCommanderLegacyVintagePauper
Not legal inBrawlStandardPioneerModern
2 printings · $0.35 to $0.79 at Card Kingdom
| Set | Number | Rarity | Card Kingdom | Foil |
|---|---|---|---|---|
| Dominaria Remastered | 33 | Common | $0.35 | $0.49 |
| Judgment | 33 | Common | $0.35 | $0.79 |
2 rulings from Wizards of the Coast
- 8 December 2022Because damage remains marked on a creature until the damage is removed as the turn ends, nonlethal damage dealt to Vigilant Sentry may become lethal if the number of cards in your graveyard falls below seven.
- 8 December 2022Once you activate the ability Vigilant Sentry gives itself, it doesn’t matter what happens to the number of cards in your graveyard. That ability will still resolve even if that number drops below seven in response.