Cheapest priced copy (Innistrad: Double Feature): $0.35 at Card Kingdom, near mint, their price list as of .
Gryffwing Cavalry 
Creature — Human Knight · 2/2 · Uncommon · Innistrad: Double Feature · #283
Flying
Training (Whenever this creature attacks with another creature with greater power, put a +1/+1 counter on this creature.)
Whenever this creature attacks, you may pay {1}{W}. If you do, target attacking creature without flying gains flying until end of turn.
Legal inCommanderPioneerModernLegacyVintage
Not legal inBrawlStandardPauper
2 printings · $0.35 to $0.49 at Card Kingdom
| Set | Number | Rarity | Card Kingdom | Foil |
|---|---|---|---|---|
| Innistrad: Double Feature | 283 | Uncommon | $0.35 | $0.49 |
| Innistrad: Crimson Vow | 16 | Uncommon | $0.35 | $0.49 |
3 rulings from Wizards of the Coast
- 19 November 2021Once a creature's training ability has triggered, destroying the other attacking creature or reducing its power won't stop the creature with training from getting a +1/+1 counter.
- 19 November 2021A creature's training ability triggers only when both that creature and a creature with greater power are declared as attackers. Increasing a creature's power after attackers are declared won't cause a training ability to trigger.
- 19 November 2021You must choose a target for Gryffwing Cavalry's last ability before you choose whether or not to pay the cost. If there is no legal target, you won't have the opportunity to pay the cost.