The Robe of Vecna is a set of robes for mages and it offers like all the robes of the aligned archmagi, a basic armor class of 5, but this robe can be used by all alignments, offers magical resistance bonus of 10%, instead of +5% and lowers the amount of time needed to cast spell by 4 units, but it doesn't offer a +1 bonus to all saving throws, which the robes of the aligned archmagi do. This item appears in BGII(SoA)BGII:EE(SoA), it's sold by Deidre in the middle of the Adventurer's Mart.