This item can be found inside the Arena Spoils in Blackrock Depths. Upon killing Theldren in BRD, the Arena Spoils chest will spawn. This weapon is one of the possible rewards from that chest. Theldren can be summoned in the Ring of Law using the Banner of Provocation and is part of the Dungeon Set 2 quest chain.
This item is the weapon of Malgen Longspear, one of Theldren's gladiators and a possible opponent in the fight against Theldren.