When cast, greater mantle protected the caster or another individual from a specific spell or spell-like effect. It absorbed the effects of the spell, or magical item discharge, then allowed the recipient of its effects to make a choice. The bearer of the greater mantle could use the absorbed magical energy to heal themself, or launch a different, specific spell towards another individual.
The spell from which the recipient was protected, along with the spell that was "reflected", were both chosen by caster during the casting of greater mantle. The latter of these spells had to be of equal or lesser power than the former.
Multiple castings of this spell could not be placed on the same individual at the same time, nor could they be combined with the effects of mantle of Mystra.
The protection conferred by the greater mantle lasted at least an hour, and was not stopped by the effects of a single spell casting. However, the protection could be removed by a single casting of dispel magic.