Missouri will by far be the best defense BYU has faced since Michigan. When BYU played Michigan, it was 12th in the S&P+ advanced metric, strength-of-schedule adjusted defensive rankings. Missouri is currently ranked 14th in those same rankings.
It all starts up front for the Tiger defense. Missouri has an outstanding four-man defensive front that is so good at getting to the quarterback that the Tigers do not blitz much. The Tiger defensive line is ranked fourth nationally in creating havoc (another advanced metric category). To counter, BYU's offensive game plan should include a heavy bevy of quick passes and pocket movement to keep the Tiger defensive line out of rhythm.