Cheapest priced copy (Forgotten Realms Commander): $0.49 at Card Kingdom, near mint, their price list as of .
Opportunistic Dragon 
Creature — Dragon · 4/3 · Rare · Forgotten Realms Commander · #134
Flying
When this creature enters, choose target Human or artifact an opponent controls. For as long as this creature remains on the battlefield, gain control of that permanent, it loses all abilities, and it can't attack or block.
Legal inCommanderPioneerModernLegacyVintage
Not legal inBrawlStandardPauper
7 printings · $0.49 to $2.49 at Card Kingdom
| Set | Number | Rarity | Card Kingdom | Foil |
|---|---|---|---|---|
| Forgotten Realms Commander | 134 | Rare | $0.49 | — |
| Throne of Eldraine | 133 | Rare | $0.49 | $0.49 |
| Throne of Eldraine | 364 | Rare | $0.69 | $1.99 |
| Throne of Eldraine Promos | 133★ | Rare | — | $0.69 |
| Throne of Eldraine Promos | 133p | Rare | $0.49 | $2.49 |
| Throne of Eldraine Promos | 133s | Rare | — | $1.79 |
| Tarkir: Dragonstorm Commander | 228 | Rare | $0.49 | — |
4 rulings from Wizards of the Coast
- 4 October 2019If another player gains control of the permanent Opportunistic Dragon has kidnapped, that permanent doesn't regain its abilities and still can't attack or block.
- 4 October 2019Opportunistic Dragon's effect doesn't expire if another player gains control of it or if it loses all abilities. The effect only expires once it's no longer on the battlefield.
- 4 October 2019If the stolen permanent normally has any abilities that would trigger when Opportunistic Dragon dies, those abilities won't trigger.
- 4 October 2019If Opportunistic Dragon leaves the battlefield before its triggered ability resolves, your opponent keeps control of their Human or artifact, it doesn't lose any abilities, and it can still attack or block as normal. You don't gain control of it at all.