I once had a supposed molly that I suspected to be piperazine + mdxx combo due to it's small size and odd color, but I did notice some fragments in the transparent capsule that were from my experience MDMA-colored, like my avatar. I tested it with my marquis, it reacted the way you describe, first rapid bubbling instantly then a yellow color to purple/black within about 3 seconds. From the bubbling instantly I suspected it was a pipe, and I took it to confirm (didn't want to waste a potentially good molly cap), it was a pipe. Felt very low threshold mdxx effects after about an hour and a shitty feeling that mixed with it in shitty(what's the opposite of harmony?). The piperazine peaked after about 2 hours, and it felt shitty as hell the whole time. Tested it with mandelin reagent too, had similar reaction. hope this helps. The bubbling/fizz should be simultaneous with color change, not before with good molly. Good molly should turn dark purple black almost instantaneously.