Maelstrom weapons are unique weapons that have a bonus which procs off a specific ability for each type of weapon (Bow, Melee, Staff). These weapons only drop from the final boss in veteran mode (one weapon per vMA completion). The drops are RNG based, with a chance to get any weapon in any trait each time you beat vMA.
For the purpose of the proc, each weapon counts as a 2-piece set. Each weapon is bound on pickup and drops in the Maelstrom motif style.
The Maelstrom's Greatsword: Critical Charge deals an additional 4300 Physical Damage over 5 seconds.