Probably mixtures of MDA, MDMA, MDE, good quality amphetamine, and caffeine (oral caffeine, not coffee caffeine; it can really do you in, and synergises well with amph).
Anybody who has read the good speed guide in naughty places, will know that at any given time out of like 50 vendors there are a maximum of 1-3 vendors who are considered worth using (coming from user reports, wedinos tests, EC tests).
Getting pure amphetamine is almost impossible, there's usually at least caffeine in there. I've had it, and seen it, but overall it's purity is never more than a maximum of iirc 40-60% or so. They're also notorious for sending high quality the first time, then the next time you get a henry of dry and a henry of wet which is a different colour and trying to fob you off when questioned. The level of bait and switch and homemade concoctions on a whim are ridiculous. I think, to be fair, they're probably sketchy speed freaks concocting their own little experiments to keep their habits going. That's how they appear to me. It's even hard to import the pure from a EU country TBF. Same thing all down the line. IMO/IME.
Ironically, the MDMA "problem" might be that it's just too damn pure these days, or was. We had no idea what we were getting in the 90's-2000's, just word of mouth on here and the streets, and anecdotal speculation based upon what we knew about the individual drugs. I'm not sure how accurate testing kits are/were but IIRC they were often indecisive with regards to colour etc.
This is the only answer I can think of to the common statement: "I always preferred old pills" when they should in theory contain the same batch, or source, of crystal MDMA.
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