XTC usually refers to MDMA in pill form, used to be contaminated/mixed with some other additives but it's largely MDMA these days.
Source https://www.drugsinfo.nl/xtc/wat-je-moet-weten-over-xtc
Source https://www.drugsinfo.nl/xtc/wat-je-moet-weten-over-xtc
Am very happy to hear this kind of thing is more rare. Not that street users have too much more assurance either way the MDMA they are getting is in fact MDMA, but hopefully thar whatever analogues there are now are a little better than meth or heroin.
Almost all Ecstasy/MDMA outside a pharmaceutical setting is adulterated, usually with other amphetamines. The degree of adulteration varies, and in some cases it may not be very noticeable by the user, but it's incredibly rare to find pure MDMA outside of a pharmaceutical setting.
Methamphetamine is one of the most common adulterants. (This is a bit of a misnomer, because MDMA is itself actually a methamphetamine, but it's not the one most people are referring to when they say "meth").
Ecstasy is almost never pure. While the degree of contamination varies and may not be subjectively noticeable by the user, the vast majority of ecstasy has some degree of adulterants in it, often other amphetamines, and sometimes other substances altogether.