Based on this hint by Zantai we can state that the other mastery is already in game (or at least its name). Can we think of iconic masteries from bosses/npcs/etc. that are not well covered yet in the current mastery set?
Outcast: Witch - the arcanist mastery doesn’t quite fit it Id say (no elemental, more towards aether & chaos). In game examples: Anasteria, Rallia.
Also the spirit guides Sahdina, - Initially I went to look up their names to put in the list of Witches, but figured it might be a unique mastery. However the first one we encounter, Sahdina, she say herself in the opening video she is only a witch.
Order of Death’s Vigil: Necromancer - cold and chaos damage, summoning skeletons - would be close to an Occultist though - Question: if it is Necromancer, how can it be different from the Occultist? Most of Death’s Vigil’s NPCs qualify under this (or a combo with another mastery)
Kymon’s Chosen: Paladin/Templar - fire and lightning - currently placed in Elementalist. Key difference that it would not be the tribal lightning throwing around we get from Shaman, nor the engineering gadgets from Demolitionist. Most of Kymon’s Chosen would fit under this (though currently they would fit under Elementalist / Commando / Warder)
Black Legion: Deathmarked - Ranged/Necromancer? - example of these are the gentleman in the pine barrens giving quests. Not very clear what their skill set would be, as they only give quests. (Then again, we also did not know much about the inquisitor - speculate away!)
Priest - the undead have quite a few of them: Grand Priest Zarthuzellan; High Priest Rolderathis - mention is made of one priest in of Kymon’s Chosen by the name of Orwell, though based on the stats of his gun he is an Elementalist (Demo/Shaman).
Witchdoctor - Groble clans all have one, though we have not seen much of its skill set, it would probably be somewhere between the Shaman and the Occultist, but without the focus on pets.
Scout - There is a scout added in the last patch, an easteregg towards the 8th class?
Archer - Quite a few around, but currently the longbow is not in game - potential for a dedicated crossbow mastery?
Skirmisher - present in the Outlaw faction. A Skirmisher class based on both shield + Gun would give us both a 3rd gun focused class (With Inquisitor looking to be a gun+spell class), AND a second shield heavy class (Soldier being the only class that has interaction with shields period atm).(Thank you Steelflame)
Tracker - present in Beastkin enemies - ranged with a net to immobilize its enemies. Inspired by TQs Hunting mastery. Focus on 2-h ranged weapon (crossbow or gun), ranged buffs and slows - possible through poison/cold (think Ice projectile - similar to how Demolitionist have fire/lighting)
Inventor - Kasparov’s side kick, but not really a mage. Perhaps the above quote only refers to the name - and would this mimic the fan made mastery with gun turrets and other steampunkish engineering that is already in game.
