Novichok

Novichok is a potion and a lethal nerve agent within the Official XNDUIW Mod, and it is a known chemical weapon, which was developed in the Soviet Union and Russia between 1971 and 1993, though it can be dispersed through ultrafine powder.

Russian scientists who actually developed the nerve agents claimed that it's the deadliest ever made, with some versions of the potion having 5x or even 8x the potency of VX, and such agents were also produced in Iran. During the 21st century, Novichok agents have been used to kill opponents of the Russian government, though attacks have been known since at least 1995.