Goblin Vandal

Oracle Text

Whenever Goblin Vandal attacks and isn't blocked, you may pay R. If you do, destroy target artifact defending player controls and Goblin Vandal assigns no combat damage this turn.

Card Rulings

4/1/2008 If the defending player controls no artifacts that you can target, the ability doesn’t go on the stack and you can’t pay .
4/15/2013 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.