Cheapest priced copy (Adventures in the Forgotten Realms): $0.35 at Card Kingdom, near mint, their price list as of .
Green Dragon 
Creature — Dragon · 4/4 · Uncommon · Adventures in the Forgotten Realms · #295
Flying
Poison Breath — When this creature enters, until end of turn, whenever a creature an opponent controls is dealt damage, destroy it.
Legal inCommanderPioneerModernLegacyVintage
Not legal inBrawlStandardPauper
2 printings · $0.35 to $1.99 at Card Kingdom
| Set | Number | Rarity | Card Kingdom | Foil |
|---|---|---|---|---|
| Adventures in the Forgotten Realms | 186 | Uncommon | $0.35 | $0.49 |
| Adventures in the Forgotten Realms | 295 | Uncommon | $0.79 | $1.99 |
2 rulings from Wizards of the Coast
- 23 July 2021Green Dragon's Poison Breath ability continues to function until end of turn even if Green Dragon is destroyed or otherwise leaves the battlefield. It takes some time for toxic gas to dissipate.
- 23 July 2021Green Dragon's Poison Breath ability is different than deathtouch. Notably, creatures still need to deal damage to a blocking creature equal to its toughness before dealing damage to another blocking creature or trampling over to a player or planeswalker.