First off, increase the charisma penalty to -2. You always have to use even numbers to make sure the penalty to skill checks and the like is always -1. I would also suggest adding another drawback, such as a -1 morale penalty on attack rolls and saving throws. As is, this spell is infringing on the power level of mind blank, and uses a much lower spell slot. Making a permanent item of this spell would be ridiculously useful for every class, except maybe sorceror, bard and paladin.