Crimson Mist is a mushroom that grows in the forests of The New Republic of Bēti, the caps of which contain a powerful performance enhancer and painkiller administered by eating the dried caps - drying the caps causes the poison, which is extremely deadly, to break down into other chemicals that cause the intended properties.
The effects of Crimson Mist include temporary muscle hypertrophy that becomes increasingly extreme as the dosage increases, increase in blood flow, massively increased production of adrenaline, and a potent painkilling property which is the most prominent property when in low dosages. If taken chronically the muscle increase can become permanent.
The negative effects, however, are just as dramatic, including violent behaviour (the infamous "berserker state" used prominently by the Blood Elf Berserkers), loss of the ability to reason and distinguish friend from foe and massive alterations in brain chemistry.
It is addictive, and long-term, it can cause permanent infertility, irreversible masculinisation in females, and insanity, with risks of cardiac problems if taken frequently in high dosage. It is legal, but highly controlled, in many nations.