Even if it was 100% Pure MDMA you can still get a comedown.
Its a serotonin releasing chemical,
Main 3 ways to avoid getting a comedown are as follows;
1. Dont redose, Take one dose and that is it
2. Dont take stupid doses, like 200mg+ , stick with between 150mg - 180mg (Depends on how good it is though i guess and how much % of the Molly is active mdma. You should know yourself what your mdma is like.)
3. Dont take it too frequently, once a month is the minimum you should leave it really. others will say more, shulgin says 90 days, I like to redose every 6 weeks
Another possible reason i put down to a comedown is drinking alcohol before, during and after a roll. Ive been around first timers. second timers , they take mdma and they get a nasty comedown but i notice they drink a fair bit,