Can we use more than 100k tris if for example we wanted to create a beauty shot with effects like embers or sparks, or maybe even extra props that aren’t necessarily part of the finished character? As long as the character by itself is less than 100k tris?
Any prop that is part of the character falls under the 100k
You can add some cards for sparks etc that don’t count towards thats.
If you want to add some secondary pieces like a base or environment pieces they won’t count towards the 100k, but also won’t factor into judging.
Only the character will.
Is fanart allowed?
So I know cards for fx won’t account into the polycount, but what about hair cards? Would that fall into the maximum polycount? 
Since the idea of warlocks may or may not involve familiars, are we allowed to model the warlock as well as any familiars they may have? Thanks 
Fanart is best avoided for copyright reasons
Everything that’s part of your character counts. So hair cards count toward polycount and texture limit
Yes, their familiar could be represented as well, but would count towards your final poly and texture budget 
Does it have to be a bad guy, or is a good guy looking character just considered a mage and not a warlock?
Can i use substance painter for rendering.
When you say you can only use two 4k map sets, does that mean you can only use two materials for your entire character?
Following up with the question from @SebLapthorne, does textures for transitional meshes and materials to blend the eyes or mouth i.e count on the 2 sets of 4k textures? how is this best approached inside the rules of the challenge?
No, you can use as many materials as you wan’t.
But those materials will be defined by your maps.
So a set would include albedo, spec, emissive, transparency etc.
And you can do that for both sets
See my reply above
No, it has to be a realtime engine of some sorts.
As far as I know, substance uses iray which is a raytracer
Bad guy
Is spotlight painting for textures inside Zbrush allowed, or does that count as a paintover?
Also, if my warlock is holding a spellbook, wand, or staff, does that count towards the triangle limit? Or if I sculpted a fireball spell, for example, does that count towards the triangle limit
Any kind of texturing is allowed. As long as you don’t “paint over” the final image.
Everything counts towards the limit.