Boon Harbinger Greatsword / Staff GW2 Harbinger WvW Builds
Harbinger is normally built to kill things. 
Dark Disciple replaces Death Shroud with 
Harbinger Shroud, which hands you offensive skills but leaves you open to attack while you use them, and stacks Blight on you the longer you stay in — Blight cuts your maximum health, so the spec is a deliberate trade of safety for output.
The build in this library takes that trade in a different direction. With Blood Magic and the elixirs, the shroud stops being a damage stance and becomes an aura: 
Deathly Haste pulses quickness and fury to you and the allies around you for as long as you are in it, and 
Life from Death heals them again every time you leave. 
Transfusion turns your Staff marks into something your allies trigger for heals, vigor and 
Stability. 
Twisted Medicine and 
Bolstering Brew hand your elixir boons and protection to everyone in the blast, and 
Ritual of Life makes reviving a body into an area rez.
It is full Minstrel's with 
Leadership and nothing on the bar that does damage on purpose — a support build wearing a damage spec's name.
1 Harbinger build
Boon Harbinger Greatsword / Staff Playing Harbinger in WvW
Blight is the cost of everything good here. You want to be in shroud for Deathly Haste, and staying in shroud steadily lowers your maximum health, which is exactly why the build wears Minstrel's and picks up 
Alchemic Vigor — vitality, plus a heal per stack of Blight. Twisted Medicine then turns that vitality into concentration, so the defensive stat is also the boon stat.
What the build asks of you is positioning, not reaction. The marks, the wells and the elixirs all land on the ground and pay out to whoever is standing on them; if the squad is not on top of you, none of it happens.
It is not defenceless — 
Elixir of Ignorance breaks stuns and gives resistance and protection — but alone it kills nothing, and the boon and rez output that justifies the slot is all output onto other people. Bring it when the squad needs another body holding it up. When the squad needs pressure instead, Scourge is the Necromancer for it.