Evil Tirek is Tirek's stronger side in the war. He flipped out whenever his close friends were in danger. While flipped out his irises turn light blue and his teeth become sharp and jagged. He displayed great skill in fighter and extra strength. He was so powerful that he caused an injury to The Tiger General himself.
Back in tree town Tirek does not flip out like other war vets, however if he sees something pervy his pupils dilate, but it is unknown why. When in this state he still seems to be in control and he does not harm others.
Evil Tirek does not really seem to be "evil" much at all. His flipped out state in the war was murderous but only to those who harmed his friends.