Quickened non-casting 0-enc guys?
Banelords need not worry about your silly fatigue, fool!
Oh, and don't forget quickening(level 7, maybe?) that quickens many squares of units. It comes late, but it really is powerful(40 quickened demon knights for t3h win).
Generally, it's the fatigue issues that make mage thugs usually a worse choice than "meat" thugs - mages look great on paper, but in use it's really difficult to manage their fatigue.