Stealth most likely considering natural invisibility. Although can perhaps function as sniper/blaster hybrid combo if he takes with sorcerer area effect spells + some ray spells and instead argent savant takes Spellwarp Sniper (http://dnd.arkalseif.info/classes/spellwarp-sniper/index.html) class. However to get most from PrC you need bit more sneak attack dice (qualification wise you can do it with feat tax with two feats; one shadow hand maneuver and martial stance; assassin stance).<br/><br/>But then again if he focuses on force spells as argent savant and just has insane AC thanks two PrC's boosting it (and getting mailed might of magelords spell, persistent if possible).