This weapon is part of the set I use for my Sevagoth's Prime Shadow Build. I'm focused on heavy attacks only after casting Embrace and Death's Harvest.
[Dispatch Overdrive] on exilus if doing heavy attacks only.
[Sevagoth's Shadow] inflicts both damage vulnerability and increases flat critical chance on Death's Harvest, but the latter depends on [Sevagoth Prime]'s ability strength, NOT the shadow's, from what I can see.