Cheapest priced copy (Iconic Masters): $0.35 at Card Kingdom, near mint, their price list as of .
Riverwheel Aerialists 
Creature — Djinn Monk · 4/5 · Uncommon · Khans of Tarkir · #51
Flying
Prowess (Whenever you cast a noncreature spell, this creature gets +1/+1 until end of turn.)
Legal inCommanderPioneerModernLegacyVintagePauper
Not legal inBrawlStandard
3 printings · $0.35 to $0.49 at Card Kingdom
| Set | Number | Rarity | Card Kingdom | Foil |
|---|---|---|---|---|
| Iconic Masters | 71 | Common | $0.35 | $0.49 |
| Khans of Tarkir | 51 | Uncommon | $0.35 | $0.49 |
| The List | IMA-71 | Common | $0.35 | — |
3 rulings from Wizards of the Coast
- 20 September 2014Prowess goes on the stack on top of the spell that caused it to trigger. It will resolve before that spell.
- 20 September 2014Any spell you cast that doesn’t have the type creature will cause prowess to trigger. If a spell has multiple types, and one of those types is creature (such as an artifact creature), casting it won’t cause prowess to trigger. Playing a land also won’t cause prowess to trigger.
- 20 September 2014Once it triggers, prowess isn’t connected to the spell that caused it to trigger. If that spell is countered, prowess will still resolve.