Invoker adds a more traditionally magical flavour to the Revenant, and a race of mistwalking spellcasters seems like the perfect fit. Also, it's another villain we get to channel (please Anet, not a third hero elite spec in a row). Fitting for a channeler of the Unseen Ones, the spec also grants access to stealth.
As to who the Mursaat legend would be specifically, I'm not sure yet. Lazarus, of course, is the obvious choice, but the fact that you could theoretically channel Lazarus when fighting against Lazarus himself could be a dealbreaker. The other option is Optimus Caliph, who seems to have been an authority figure among the Mursaat.
F2 Jade Construct: You summon a jade construct depending on your current weapon; a melee Jade Armor when you have a ranged weapon, or a ranged Jade Bow when you have a melee weapon.
F3 Only becomes active when you have an active jade construct. You command your construct to deliver an attack:
Main-hand scepter as a ranged weapon with an emphasis on zone control.
Skill 1: A standard projectile, but when it hits a foe, it creates a rift at their location. The rift explodes after a short delay, dealing area damage.
Skill 2: Summon a fireblast from the mists that strikes a targeted area dealing damage and applying chill and blind. (Blast Finisher). Stores 2 charges.
Skill 3: Create a circle for a few seconds that deals damage every second. Foes that cross the perimeter are inflicted with torment. (Dark Field)
Similar to Engineer's AED. Lazarus could revive by storing his essence into vessels, so Invoker borrows that same trick to cheat death.
Utilities. The utilities are ground-targeted abilities based on the weapons and tools utilised by the Mursaat.
This is the upkeep skill of this legend, and as long as it's active, you are stealthed. You can use it for a maximum of 4 seconds, at which point it automatically detoggles. It also detoggles when you get revealed, or make an attack. In the last case, when you make an attack while stealthed, enemies you hit with that attack are tethered with Spectral Agony.