Mindstab Thrull

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

Masters Edition

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

Fifth Edition

Sacrifice Mindstab Thrull: Defending player chooses and discards three cards. Use this ability only if Mindstab Thrull is attacking and unblocked.

Fallen Empires

If Mindstab Thrull attacks and is not blocked, you may sacrifice it to force the player it attacked to discard three cards. If you do so, it deals no damage during combat this turn. If that player does not have enough cards, his or her entire hand is discarded.

The defending player gets to choose which cards they discard.

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.