Tetarti is the fourth strain of GUILT encountered in Under the Knife and Second Opinion. Greg Kasal is the first known host of Mature Tetarti. Upon learning that it is not treatable, Derek and Angie set out to find the antigens required to fully treat mature Tetarti. While immature Tetarti attacks alone, mature Tetarti comes in trios, initially appearing as types V, P, and H, colored purple, green, and yellow, respectively.