Cheapest priced copy (Avacyn Restored): $0.35 at Card Kingdom, near mint, their price list as of .
Joint Assault 
Instant · Common · Avacyn Restored · #183
Target creature gets +2/+2 until end of turn. If it's paired with a creature, that creature also gets +2/+2 until end of turn.
Legal inCommanderModernLegacyVintagePauper
Not legal inBrawlStandardPioneer
1 printing · $0.35 to $0.49 at Card Kingdom
| Set | Number | Rarity | Card Kingdom | Foil |
|---|---|---|---|---|
| Avacyn Restored | 183 | Common | $0.35 | $0.49 |
2 rulings from Wizards of the Coast
- 1 May 2012Joint Assault targets only one creature. If that creature is an illegal target when Joint Assault tries to resolve, it won’t resolve and none of its effects will happen. No creature will get +2/+2.
- 1 May 2012Joint Assault checks whether the target creature is paired only when it resolves. If it becomes unpaired later in the turn, neither creature will lose the bonus. Similarly, if it becomes paired later in the turn, the creature it’s paired with won’t gain the bonus.