Why would Mo need a diuretic? He weighs 218lbs soaking wet, should be an easy cut.
Maybe he got injured?
Masteron isn't purely a diuretic, it's an androgen and gives a bunch of benefits to an athlete, especially when stacked with other substances. My guess is he was using a cocktail of stuff and the Masteron was the thing that he cycled wrong so that's what showed on the test.