Roekillik watchers will run from the player once the player enters their aggro radius. As they run away, every mob whose aggro radius they pass through will attack the player. They can be stopped from running by being attacked.
Once down to approximately 10% of its life, a roekillik watcher will use an ability that causes certain other mobsto aggro the player, regardless of where they are in the zone. Which mobs called depends on the particular roekillik watcher. For example, the roekillik watcher at the very entrance of The Icy Dig will call Patrolman Skzza and Bobo. The ability has a casting time, and the roekillik watcher can potentially be killed before executing it.