I think they get both war paint and scars. The scars seem to be a similar format as the Night Elf ones, separated in some sort of b&w map, rather than attached to particular faces. I would assume the war paint will work like troll war paint.
- - - Updated - - -
I really hope Mag'har get Shattered Hand skins with one arm lacking. A few builds ago, before Forsaken got 3 different rot choices, they had the choice to toggle rot in specific areas (arms, legs, body), this kind of indicates to me that they could do the same with Shattered Hands arms, or, if Mechagnomes hadn't been an allied race, gnome limbs.
They could do that and have it so that weapons can be equipped on that side (for stats) but not seen. If not being able to see boots, pants and gloves on Mechagnomes is alright, I'm sure not being able to see one weapon is fine too.
- - - Updated - - -
Trolls really could use more. Both male and female need ear options and males need beards.