Cheapest priced copy (Fifth Edition): $0.35 at Card Kingdom, near mint, their price list as of .
Necrite 
Creature — Thrull · 2/2 · Common · Fifth Edition · #181s
Whenever this creature attacks and isn't blocked, you may sacrifice it. If you do, destroy target creature defending player controls. It can't be regenerated.
Legal inCommanderLegacyVintagePauper
Not legal inBrawlStandardPioneerModern
5 printings · $0.35 to $0.49 at Card Kingdom
| Set | Number | Rarity | Card Kingdom | Foil |
|---|---|---|---|---|
| Fifth Edition | 181 | Common | $0.35 | — |
| Fifth Edition | 181s | Common | — | — |
| Fallen Empires | 41a | Common | $0.49 | — |
| Fallen Empires | 41b | Common | $0.35 | — |
| Fallen Empires | 41c | Common | $0.35 | — |
One ruling from Wizards of the Coast
- 15 April 2013An ability that triggers when something “attacks and isn’t blocked” triggers in the declare blockers step after blockers are declared if (1) that creature is attacking and (2) no creatures are declared to block it. It will trigger even if that creature was put onto the battlefield attacking rather than having been declared as an attacker in the declare attackers step.