Cheapest priced copy (Battlebond): $0.35 at Card Kingdom, near mint, their price list as of .
Tandem Tactics 
Instant · Common · Ravnica: Clue Edition · #76
Up to two target creatures each get +1/+2 until end of turn. You gain 2 life.
Legal inCommanderPioneerModernLegacyVintagePauper
Not legal inBrawlStandard
5 printings · $0.35 to $0.49 at Card Kingdom
| Set | Number | Rarity | Card Kingdom | Foil |
|---|---|---|---|---|
| Battlebond | 112 | Common | $0.35 | $0.49 |
| Battle for Zendikar | 52 | Common | $0.35 | $0.49 |
| Ravnica: Clue Edition | 76 | Common | $0.35 | — |
| Jumpstart | 135 | Common | $0.35 | — |
| The List | BBD-112 | Common | $0.35 | — |
One ruling from Wizards of the Coast
- 25 August 2015You can cast Tandem Tactics with no targets. When it resolves, you’ll gain 2 life. However, if you cast Tandem Tactics with any targets and all of those targets are illegal as it tries to resolve, it won’t resolve and none of its effects will happen. You won’t gain 2 life in that case.