Corrupted Primal Obelisk

The Corrupted Primal Obelisk is a placable obelisk that will shoot enemies within range. With only one target, the damage may be mediocre, but with many enemies in range and a short cooldown, the item quickly proves it's worth.

Source
This item is looted from the Mysterious Corrupted Obelisk in the Vault of the Earth in Tanaan Jungle. The item is hidden behind a wall of fire, which is opened up in the final chapter of the Garrison Campaign, allowing entry into the cave. Many classes, however, have ways of passing through the fire prior to reaching that point in the quest chain.
 * Mages can Blink through.
 * Druids can Displacer Beast through.
 * Warlocks can use their eye of Kilrog and then place a portal behind the fire.
 * Rogues can shadowstep to mages and druids if they duel them.