A highly addictive drug, in the form of crystals. It was invented by the Nazis, makes you jittery as fuck, and two of its ingredients are drain fluid, and cat litter. Oh, and it fucks up your body. You get scabs from picking out the bugs that you think are under your skin, your teeth and hair fall out. The pony in the comic has been "tweeking" ( the term for doing meth) fora few weeks, judging by the state of his mane, and missing a tooth or two. You do shit that's completely not normal. Meth is one hell of a drug, very damaging to the body. And yes, it really was invented by the Nazis.