- Usually human apprentices of great Thousand Sons sorcerers. - Builder unit, able to initiate the materialization of all structures; takes up no pop cap but have limited availability. - Can capture or uncapture Strategic Locations, a significant task assigned only to the lowest-ranked members of the army. - Can repair Vehicles and structures; the bigger the squad size, the faster the rate. - Place sorcery tomes to commence Building construction. Can walk away once set in place and Building will complete itself. - Have various minor psychic powers, but sometimes the power of their spells is too great for the casters to endure! - Thralls act as an occult witch coven, so their spells recharge faster, as the squad size increases! - Effective against Infantry.