Whenever Farrel's Zealot attacks and isn't blocked, you may have it deal 3 damage to target creature. If you do, Farrel's Zealot assigns no combat damage this turn.
10/4/2004 In a multiplayer game, the target creature does not need to be one of the ones controlled by the player you actually attacked.
10/1/2008 This ability resolves during the declare blockers step. If the damage dealt this way is enough to destroy an attacking or blocking creature, that other creature won’t be around to deal its combat damage.
10/1/2008 If there are no other creatures on the battlefield, Farrel’s Zealot will have to target itself. Of course, you can choose not to use the ability when it resolves.
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.