Feeblemind

The spell Feeblemind is among the U5's official list of banned incantations; using the spell in a non-government sanctioned situation will very easily result in life imprisonment depending on the jurisdiction. 
Ever since the Provincial Democratic Conclave of Tempora banned capital punishment, this spell has been used in its stead. Various mortal rights activists have deemed this spell a "fate worse than death", but no action has been taken on the part of Enobaria Monmouth to rectify this.

Effect

The major effect of Feeblemind is that it ensures the temporary death of an individual's sentience. Your intelligence and identity are reduced to no more than that of a cornered animal, rendering you unable to speak, think, or understand who you are.