It halves normal/support PPC damage, rounded down to a minimum of 1 point.
Downside, you can only use it without any problems for six turns (total, not consecutive).
So if you know your opponent likes PPCs, it can be pretty useful - turning a PPC hit into an ML hit.
Add Reflective Armour and your opponent won't be happy (ever seen an Awesome or a Hellstar cry?).