King Virus (キングウイルス, Kingu Uirusu) is a hybrid of the three types of Dr. Mario's viruses created by Kamek in Super Mario-kun. It is a giant virus with elements from each virus: Yellow's snout and horns, Red's mouth, and Blue's eyebrows.
To stop Mario, Kamek creates King Virus, a super virus that only affects humans (though it does give Bowser a small cold), and launches it towards Mario, landing it right into his mouth. Suddenly, Mario starts feeling so weak and cold that Yoshi's fire breath cannot warm him up. While Yoshi fights with a Diggin' Chuck, Mario keeps dripping nasal mucus and, after Yoshi defeats the enemy, sneezes so hard that the King Virus is ejected on a river of nasal mucus.