Note that the Quest Helper is accurate. In the quest window, the Slygie kill count is recorded in the Petrifighter kill count. In other words, the correction in the below screenshot should be Petrifighter 0/100 and Slygie 100/100. This quest was started after having completed all krex prequests. After going further, I have confirmed that killing Petrifighters will up the Slygie kill count in the quest window.
