The X Virus is a virus developed by X to take control of people's minds and bodies. It plauges the Mushroom Kingdom in both The X Virus and Super Mario: Dark Times. Upon getting the virus, the victim's face turns red, but after a while, the victim's entire body will become red.
It is unknown when or how X created the virus, but MarioGame2222 confirmed it'll be revealed in Episode 9 or 10 of Dark Times.
- The X Virus inspired by the N Virus, a virus in MarioMario761's Super Mario: Next Generation.
- The X Virus also inspired The2Hunters to create the The S Virus. (The Shroob Virus)