Leash Mechanic is a mechanic used on all mobs and bosses within the dungeons. It restrains mobs from going to far from where they spawned.
The Leash Mechanic activates when a mob moves too far away from it's spawn point. The mob is then teleported back to its original spawn. Demonstrated in The Sanctuary, the mob retains all velocity in the event it was falling and it takes massive fall damage. It is also present in the fight with Zhall, since he tends to fling himself off the edge a lot. Be careful when he is leashed back into position, for this can catch a lot of players by suprise and occasionally get an unlucky stun.