A lot of scientists discovered a weird thick substance around the world that is extremely dangerous, contagious and recommended avoiding every contact with this liquid. This strange discovery was named the mutation liquid, as its name says contains a lot of mutation properties. Basically, this phenomenon seems to permanently transform people into monsters mutating their DNA, causing transformations like gaining or losing weight, sex changes, appearances or disappearances of extra limbs or body parts (such as multiple arms, heads, breasts, or genitals), merging with other people or animals into your body or transforming they in your body parts, and even the appearance of sudden animal parts in the body, causing all these aberrations to result in mutant humans with extra body parts, humans transformed into anthro or feral animals human-animal chimeras. The people can be affected by this by only having contact with the liquid or having sex with someone already transformed. Also, this liquid along with the transformations make the people horny, boosting to the limit their lust desires and wanting to transform untransformed people, also recently was discovered that some people are transformed into the monster of their sexual fantasies, and rarely are found shapeshifters that can temporarily change their monstrous appearance at will.
Unfortunately, an evil secret corporation managed to steal this liquid and make people transform into sexual monsters just for fun, no member of this company has been found as they transform people by secretly putting the liquid in drinks, perfumes, pools, handwashes, and other media.