Cheapest priced copy (Ravnica: Clue Edition): $0.35 at Card Kingdom, near mint, their price list as of .
Thunder Drake 
Creature — Elemental Drake · 2/3 · Common · The List · #WAR-73
Flying
Whenever you cast your second spell each turn, put a +1/+1 counter on this creature.
Legal inCommanderPioneerModernLegacyVintagePauper
Not legal inBrawlStandard
3 printings · $0.35 to $0.49 at Card Kingdom
| Set | Number | Rarity | Card Kingdom | Foil |
|---|---|---|---|---|
| Ravnica: Clue Edition | 102 | Common | $0.35 | — |
| The List | WAR-73 | Common | $0.35 | — |
| War of the Spark | 73 | Common | $0.35 | $0.49 |
2 rulings from Wizards of the Coast
- 3 May 2019Thunder Drake must be on the battlefield in order for the ability to function. Notably, the ability won’t trigger if Thunder Drake is the second spell you cast in a turn.
- 3 May 2019Thunder Drake’s ability can trigger only once each turn. The ability will resolve before the second spell resolves. It doesn’t matter if the first spell you cast that turn has resolved, was countered, or is still on the stack.