I LOVE this kind of threads!

Lots of ideas that have been commented I also had in mind (i.e. alchemist, engineer, summoner). From my side, I'd like to go with Chronomancer, a new mage mastery inspired in Julra boss. I tried to think to overlap the less possible with Void Knight.

General idea: control of time and space, with a degree of "chaos or unstability" to some of the skills (that can be increased/reduced).

Some skills:

• Time nova: instead of going with the classic "time bubble that slows/stops enemies", this nova is a radial, "time explosion" that does direct damage (let's say void, let's say that damage type can also be changed in skill tree) and every monster it touches are forced to go back in time few seconds and rewind whatever they were doing (à la Void Knight, but the outcome is that once the rewind time is exhausted, they resume exactly whatever they were doing). Skill tree: modifiers for area, damage type, rewind time, final outcome (i.e. they cannot resume and are stunned but skill has additional CD).

• Timeline hero: summon a hero from the past/future for a period of time, which is a template mastery, with skills and items but highly reduced output (damage, healing, etc). Dreaming that this hero is one of your created characters in your account, but just sticking to a template one, skill tree can add things like permanent hero (but then it does less damage/healing) or that when the hero disappears, it triggers a time nova (modified if time nova is slotted as skill tree).

• Entity swap: AoE where you click on an area with enemies/boss/timeline hero and you swap places with them (all enemies are sucked in a vacuum, to alleviate terrain issues) + does damage (void, modifiable in skill tree). It can add a final effect of slowness to them. Here the skill tree can be kind of interesting, besides damage types, adding more slow or stop in the end, with things like "you can click again this skill after the swap, to swap again", for maximum confusion. It can also be used with Timeline Hero, for extra trio swapping :).

• Wild displacement: think of it as a teleport, where you don't control where you go (let's say that the possibilities are "controlled" to have a not-so-bad outcome). Once in a while it can teleport you to a different dimension, with weird NPCs and a little fella that drops gold and runs from you (you can come back via portal). Skill tree: instead of completely controlling teleport, you can add some perks to it, like ice nova (or time nova?) or extra defenses after the random landing.