Pure Evil Villains who are parasites. Germs, bacteria, and other microorganisms can count - while parasitic entities are often seen as difficult to apply for pure evil since often their dependency on others is that of survival (no matter how gruesome) and that's even mentioning the chore it is to discern whether their behavior is a natural part of their species' life cycles or is entirely their own fault, there are ways parasites can become purely evil, for example if they take far more than they require to simply survive, if they take pleasure in harming others needlessly, are sapient while their host is also sapient, and if they pursue a parasitic existence even when their kind does not require it (but simply out of a twisted desire for power over others or other vice).

The worst type of parasite (and also the one most guaranteed to be labeled as Pure Evil) is a parasitoid, a type of parasitic species that not only feeds off another life-form, but actively kills (or tries to kill) the host they're living with. In fact, more than 75% of all unambiguously villainous parasites approved as Pure Evil fall under this category, despite almost always being simply referred to as standard parasites.