I had heard on the Khador forums that the attack made with Watcher doesn't have to target the model that triggered it. But I reread the rule recently and I don't think that is correct.
(Emphasis mine)"When an enemy model advances and ends its movement, blah blah. That warjack can immediately make a full advance and then can make one normal melee or ranged attack targeting the enemy model. The attack and damage rolls against that model are boosted."
So, does watched have to target the enemy model that advanced and triggered it?