Need help trying to diagnose overheating issues.

I helped my friend build a PC and he's having heating issues and crashing because of it. Originally when we set it up his pc would idle at 60c which still seemed high to me, after about a month it started idling higher at about 78c, and would quickly rise when trying to run games. Today we tried re applying new thermal paste, made sure there was no plastic in weird places that we might have missed on setup, and there's wasn't any obvious issues. After replacing the thermal paste though it started idling cooler again at about 50c but he told me that when he tried playing destiny tonight it crashed at a high of 90c. The AIO is set to pull air from the interior of the case and push it out of the top, but radiant temp of the case seems to stay pretty cool.

His build list: https://pcpartpicker.com/list/Z9Bq8Q