Viper is a good 2nd 'real' spellcaster unit for zergs....but it seems i read somewhr bcoz viper can grant detection to units and it probably by itself is a detection unit, overseer is going to be removed....overseer is freaking cheap to upgrade rite now....by doing this i expect in the HOTS cloak banshee and even ghost rush is going to be much2 more viable again vs zerg. because spellcaster unit gas cost wont be cheap, n it will take sometime for zerg to upgrade n get them. this is my experience wif terran juz to get that raven out.