What is going on with BL these days??
Pullstring that's a lot of bullshit in one post.
"speed up meto could have an effect on your brains seratonin" Ick.
First of all, it's serotonin. "fat burners" are usually CNS stimulants of some kind, ephedrine for example. These increase metabolism and overall arousal levels, burning more calories thus burning fat in the long run. CNS stimulants raise blood pressure levels, heartrate, etc. etc.
So mixing it with MDMA, another stimulant, is certainly not a good idea. Anyway, if you're relatively young and fit, this should not be an issue. Many pills contain different stimulants in them already. Cytomel, is a thyroid gland stimulant, causing artificial hiperthyroidism thus raising metabolic rate by a lot. I don't really know how this particular compound is metabolized, or by what enzymes, so I wouldn't be sure about how it would affect the breaking down of MDMA in your body.
about the peeing comment: Bullshit, anything that is in your bladder has been already metabolized and if some % of MDMA is still present (usually MDA, one of its metabolites) will not be absorbed by retaining urination.