Energy Negation, Greater

Level: 5
Duration: 5 rounds
Saving Throw: None
Normal: Your utterance renders your target impervious to harm from one type of energy.
A nimbus of golden power surrounds your target, granting him immunity to one type of energy. 
Reverse: You wreathe your ally in energy that lashes out at those who strike him in battle.
This utterance wreathes your target in a type of energy chosen by you when you speak this utterance (acid, cold, electricity, or fi re). This energy causes damage to each creature that makes a successful melee attack against the subject of the utterance. Any creature that damages the subject with its body or a handheld weapon deals normal damage, but at the same time, the attacker takes 20 points of energy damage. Creatures wielding weapons with exceptional reach, such as longspears, are not subject to this damage if they attack the subject.