These skeleton shaman spawn with packs of Skeletal Archers and Skeletal Shieldman for protection. The Summoners are larger than regular skeletons, and have glowing purple/pink orbs around their upper bodies. These may be shields, decoration, or an indication what type of elemental damage they deal. During battle the summoners stay to the rear of their foot soldiers, where they keep busy summoning fresh skeletons, or hurling purple projectiles at any players who stray into range.
Their summoning animation is interesting; in the WWI 2008 movie they were seen shooting a purple laser beam from each eye. The beams traveled some distance, then converged and dove into the ground, causing a new skeleton to rise up a second later. It's not known if they have the ability to buff their skeleton followers, or can only create new ones.
Media
[See screenshots and concept art of the skeletal summoner in the Image Gallery.
Launching the pink (ethereal) projectile.