This set piece is a bow in the Maelstrom style.
2 items: Increases the damage Volley deals by 10-430 each tick. This bonus increases by 3-143 every time Volley ticks, up to a maximum of 8 times.
The set consists of a Bow in all traits.
While the description states that 2 items are required, this is because bows are 2-handed weapons, and thus count as 2 items by themselves, so only 1 item is actually needed.