I only did a bit of messing around of the Specter but I really love the idea and can't wait to play it for real! This is the first time since the game released I've wanted to really play Thief!
I think having so much single target could be an issue with it since while the single target heal is strong it means you will need to either focus on one target or get good at quickly swapping between targets. If the auto attack was weaker but pierced and hit three targets similar to the duel skill with pistol that could help alleviate some only healing one person issue. Maybe do the same with shroud, make it weaker but have three tethers? This would mean applying more venom though so I guess that would also need to be made a bit weaker?
The duel skill for dagger also feel like it is much worse than the pistol one. It costs less initiative and is faster since it is one skill that isn't a channel but the pistol duel skill feels like it is always the superior option. Dagger dual skill is single target while the pistol dual skill can hit three targets and gives a lot of quickness, why wouldn't I want to use the pistol one?
This is more of a question, but does the venom Specter puts on allies when healing them count as a venom for the venom life steal trait? I think it does but it's really hard to tell and the game doesn't give any indication to whether or on it is giving the life steal damage and healing.
Also probably being worked on but the game seems super conflicted with how it interprets at least some NPCs. Using skills on Lion's Arch NPCs doesn't heal them but also only triggers some of the steal effects. The scepter in general is really wonky when using abilities on them and in the case of the dagger dual skill totally breaks the projectile.