Had a track mastered, mastered track sounds way muddier than the final mix pre-mastering

Is this due to my poor mixdown only being brought out in the master? Or is this potentially a bad master?

Submitted December 21, 2016 at 12:48PM by owenbenson https://www.reddit.com/r/edmproduction/comments/5jkkoc/had_a_track_mastered_mastered_track_sounds_way/?utm_source=ifttt

Javier Rodriguez