Overwatch gives them the ability to stand and shoot when charged if there is a Greater Good Hero nearby. I've been trying to focus on Battle Traits making heroes matter (as they do in the official AoS rules so far). In this instance, when a Greater Good unit is charged, if there is a Greater Good Hero within 8" of the charging unit, they can attack as if it were the shooting phase, but at a -1 penalty to hit. I'll probably have to playtest this one to see if it's too potent, but I've chosen my words carefully in this ability and in the Markerlight rule that appears on many warscrolls so that markerlights cannot be used during overwatch.
Their other Battle Trait is an expanded use of Markerlight Tokens, so they can now use them to wreck up a unit's Bravery, improve their rend, improve their rolls to wound, and to fire seeker missiles into the unit.