Cheapest priced copy (Adventures in the Forgotten Realms): $0.35 at Card Kingdom, near mint, their price list as of .
Blue Dragon 
Creature — Dragon · 5/5 · Uncommon · Adventures in the Forgotten Realms · #289
Flying
Lightning Breath — When this creature enters, until your next turn, target creature an opponent controls gets -3/-0, up to one other target creature gets -2/-0, and up to one other target creature gets -1/-0.
Legal inCommanderPioneerModernLegacyVintage
Not legal inBrawlStandardPauper
2 printings · $0.35 to $1.49 at Card Kingdom
| Set | Number | Rarity | Card Kingdom | Foil |
|---|---|---|---|---|
| Adventures in the Forgotten Realms | 49 | Uncommon | $0.35 | $0.49 |
| Adventures in the Forgotten Realms | 289 | Uncommon | $0.39 | $1.49 |
2 rulings from Wizards of the Coast
- 23 July 2021The last two targets are optional, but the first target is not. If an opponent has at least one creature the ability could target, you must choose a target to get -3/-0. (Note that the last two targets can be any creature, not just one an opponent controls.)
- 23 July 2021Blue Dragon's Lightning Breath ability cannot target the same creature multiple times.