Cheapest priced copy (Fifth Edition): $0.35 at Card Kingdom, near mint, their price list as of .
Mindstab Thrull 
Creature — Thrull · 2/2 · Common · Fallen Empires · #40b
Whenever this creature attacks and isn't blocked, you may sacrifice it. If you do, defending player discards three cards.
Legal inCommanderLegacyVintagePauper
Not legal inBrawlStandardPioneerModern
5 printings · $0.35 to $0.49 at Card Kingdom
| Set | Number | Rarity | Card Kingdom | Foil |
|---|---|---|---|---|
| Fifth Edition | 178 | Common | $0.35 | — |
| Fifth Edition | 178s | Common | — | — |
| Fallen Empires | 40a | Common | $0.39 | — |
| Fallen Empires | 40b | Common | $0.35 | — |
| Fallen Empires | 40c | Common | $0.49 | — |
2 rulings from Wizards of the Coast
- 4 October 2004The defending player gets to choose which cards they discard.
- 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.