Cheapest priced copy (Avacyn Restored): $0.69 at Card Kingdom, near mint, their price list as of .
Essence Harvest 
Sorcery · Common · Avacyn Restored · #100
Target player loses X life and you gain X life, where X is the greatest power among creatures you control.
Legal inCommanderModernLegacyVintagePauper
Not legal inBrawlStandardPioneer
1 printing · $0.69 to $13.99 at Card Kingdom
| Set | Number | Rarity | Card Kingdom | Foil |
|---|---|---|---|---|
| Avacyn Restored | 100 | Common | $0.69 | $13.99 |
2 rulings from Wizards of the Coast
- 1 May 2012The value of X is determined when Essence Harvest resolves. If you control no creatures that time, no life will be lost or gained.
- 1 May 2012Essence Harvest targets only the player. It doesn’t target any creatures. If that player is an illegal target when Essence Harvest tries to resolve, it won’t resolve and none of its effects will happen. No life will be lost or gained.