Cheapest priced copy (The List): $0.35 at Card Kingdom, near mint, their price list as of .
Battle Mastery 
Enchantment — Aura · Uncommon · Duel Decks: Heroes vs. Monsters · #27
Enchant creature
Enchanted creature has double strike. (It deals both first-strike and regular combat damage.)
Legal inCommanderPioneerModernLegacyVintage
Not legal inBrawlStandardPauper
6 printings · $0.35 to $4.49 at Card Kingdom
| Set | Number | Rarity | Card Kingdom | Foil |
|---|---|---|---|---|
| Battlebond | 89 | Uncommon | $0.49 | $4.49 |
| Duel Decks: Heroes vs. Monsters | 27 | Uncommon | $0.39 | — |
| Dragons of Tarkir | 7 | Uncommon | $0.49 | $1.99 |
| Lorwyn | 5 | Uncommon | $0.49 | $2.99 |
| Magic 2015 | 4 | Uncommon | $0.39 | $2.49 |
| The List | BBD-89 | Uncommon | $0.35 | — |
One ruling from Wizards of the Coast
- 18 July 2014If a creature loses double strike after dealing combat damage in the first combat damage step, it won’t assign combat damage in the second one.