Mindstab Thrull (5ED)

Creature — Thrull

Whenever Mindstab Thrull attacks and isn't blocked, you may sacrifice it. If you do, defending player discards three cards.

2/2

Heather Hudson
178s/455
uuid: ecd058d3-48e9-5947-b1d3-01298f9cf023

2004-10-04:
The defending player gets to choose which cards they discard.
2013-04-15:
An 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.