Heal Specter Scepter & Pistol GW2 Specter WvW Builds
Specter is the Thief that heals. 
Steal becomes Siphon, which tethers you to an ally instead of robbing a foe, and the profession's shroud is an ally-facing weapon bar rather than a damage one: 
Grasping Shadows cleanses, 
Dawn's Repose hands out barrier, 
Mind Shock stuns enemies and gives nearby allies 
Stability.
The Wells are why it works in a zerg. Each one shadowsteps you to the point you aimed at and drops its effect there — 
Well of Gloom heals, 
Well of Bounty gives boons, 
Well of Silence strips conditions, 
Shadowfall drags a group into the middle of your squad. You do not have to be standing in the pile to land any of it, and 
Traversing Dusk turns the arrival itself into a heal.
Our one Specter is a full Minstrel's zerg healer on double Scepter/Pistol — no offensive stat on the gear at all. It is a zerg build and nothing else. Roaming with it is pointless, and in a havoc group you will keep everyone alive while nobody kills anything.
1 Specter build
Heal Specter Scepter & Pistol Playing Specter in WvW
The spec's mechanic is shadow force and the tether. Spending initiative builds shadow force, 
Enter Shadow Shroud spends it, and entering the shroud locks you onto one ally who gets barrier and then gets the stronger half of every shroud skill — Grasping Shadows heals and cleanses them specifically, Dawn's Repose and Mind Shock single them out again. So you are running two support jobs at once: the area one, and the one person you picked. Picking the right tether is most of the skill in the build.
Siphon is the other rhythm, and it is the boon output. 
Sleight of Hand and 
Lead Attacks both cut its recharge, so it comes round often: every cast is 
Fury, 
Might and 
Swiftness from 
Thrill of the Crime, 
Vigor and stolen boons from 
Bountiful Theft, and a cleanse from 
Shallow Grave.
Where it struggles is the gap. The Wells are the entire kit — healing, boons, cleanse and the pull are all Wells — and between casts a Minstrel's Scepter/Pistol is doing very little for anyone. It also gives the squad one Stability skill, Mind Shock, and it sits behind the shroud. A squad that needs Stability held up needs another source for it.