http://bgtscc.net/viewtopic.php?f=7&t=25108
Mastery of Counterspelling and Spell Turning - These abilities allow you to turn your defense into your offense. If you succesfully counter an incoming spell you can turn it back upon the caster. This only works with targeted spells though. It does not work with RTAs, AoEs, dispels, or "effect" spells. Still, there are a host of spells which can be very dangerous which can be turned including Bigby's, Flame Arrows, Magic Missiles and Magic Missile Storms. If you're facing a counterspeller don't use these spells. If you are the counterspeller you're hoping your enemy is dumb enough to use them.