Cheapest priced copy (Starter Commander Decks): $0.79 at Card Kingdom, near mint, their price list as of .
Windreader Sphinx 
Creature — Sphinx · 3/7 · Rare · Foundations Jumpstart · #391
Flying
Whenever a creature with flying attacks, you may draw a card.
Legal inCommanderPioneerModernLegacyVintage
Not legal inBrawlStandardPauper
6 printings · $0.79 to $4.49 at Card Kingdom
| Set | Number | Rarity | Card Kingdom | Foil |
|---|---|---|---|---|
| Foundations Jumpstart | 391 | Rare | $0.99 | — |
| Jumpstart | 194 | Rare | $0.99 | — |
| Magic 2014 | 81 | Mythic | $1.79 | $4.49Out of stock |
| Core Set 2019 | 84 | Rare | $1.49 | $2.49Out of stock |
| Core Set 2019 Promos | 84s | Rare | — | $2.49Out of stock |
| Starter Commander Decks | 64 | Rare | $0.79 | — |
3 rulings from Wizards of the Coast
- 13 July 2018It doesn't matter who controls the creature with flying or which player or planeswalker that creature is attacking. Windreader Sphinx's controller is the player who may draw a card.
- 13 July 2018Windreader Sphinx's ability will trigger when it itself attacks.
- 13 July 2018The creature must have flying immediately after being declared as an attacking creature in order for Windreader Sphinx's ability to trigger. For example, attacking with Kitesail Corsair will cause the ability to trigger, and attacking with Pegasus Courser and a creature without flying will cause the ability to trigger only once.