The user can generate diseases and viruses, including mixing illnesses together or creating completely new ones, whether by drawing them from already existing sources, or by manifesting them anywhere they want.
Mary (Fairy Tail) can use Anomaly Magic to create viruses with different effects such as dedication and brain damage.
Poison Ivy (DC Comics)
Death of Final Horsemen (Marvel Comics)
Famine of the Final Horsemen (Marvel Comics)
Plague (Marvel Comics) as the Horseman Pestilence.
Discord (My Little Pony: Friendship is Magic) induce Blu-Flu on Applejack and Rarity
Alex Mercer (Prototype)
SpongeBob SquarePants (SpongeBob SquarePants) releasing a breath of collected disease.
Pestilence (Supernatural) is capable of inducing any disease into humans instantly.
Catagion (Valkyrie Crusade) generates and spreads the felinavirus, a virus that turn others into cats and cat-hybrids, the virus being powerful enough to affect even supernatural entities, such as demons.