I believe the 8th mastery will be “spirit guide”. To me it would fit a Grim Dawnian take on Necromancer, support cold (spirit), vitality with its decay and pets! Undead skeletons, aether gouls etc. And since the mastery works FOR humanity, But dabbles in forbidden arts, thus vindicating… Inquisitor+spirit guide= vindicator
Edit: http://www.dictionary.com/browse/vindicator
Edit 2: crucible also has a spiritguide available, might indicate it is a class. Also, never played TQ, But I believe a class there is a spirit/dream guide class/mastery? No?