Complex sentence: They failed to improved their previous season record of 10-6 where they advanced to the playoffs for the first time since 2008 and were eliminated from the postseason after losing to the Kansas City Chiefs in Week 16.
Split into simpler sentences: They failed to improve on the previous season's record of 10-6 where they advanced to the playoffs for the first time since 2008. The Dolphins were eliminated from the postseason after losing to the Kansas City Chiefs in Week 16.