Nihilego appeared in 2016 video game called Pokémon Sun & Moon. Nihilego is a Parasite Pokémon. Nihilego, one of the mysterious Ultra Beasts, can apparently infest other beings and incite them to violence. Research is inconclusive as to whether this Pokémon can think for itself, but it sometimes exhibits the behavior of a young girl.
Nihilego is an Ultra Beast that resembles a jellyfish. The bell is semi-translucent and encircled with several white, star-shaped markings. The wavy rim of the bell flares outward and is bright blue. Its tentacles appear gelatinous and give it a vaguely humanoid shape. Several tentacles mesh together forming the appearance of cape or long hair, while four shorter tentacles resemble shorter hair and arms. Two long tentacles make up the legs of the human-shape. In addition to its shape, it is sometimes seen acting like a young girl.
Nihilego is a parasitic organism and, by latching onto one's head, is capable of injecting a neurotoxin that subtly alters the thoughts and actions of any human or Pokémon that becomes its host. This neurotoxin stimulates intense feelings of excitement while causing a loss of inhibitions, which acts to forcibly bring out any latent potential within the host while wearing away at their minds. Nihilego's exact levels of intelligence are unknown, but according to Wicke, the Aether Foundation's research it seems to act mainly on a self-preservation instinct. In its home dimension, the anime shows that Nihilego can control its environment.
As shown with Lusamine, Nihilego is capable of physically merging with a host. In this "merged" state, the bell loses its stars, developing several iridescent spots across its surface. The host's body is visible within the bell with their legs dangling beneath it. Its eight tentacles become long and flattened and have numerous deep black spots with various colored diamond-shapes inside. Four of the tentacles are connected to the bell via frilly white structures; these tentacles have four spines protruding from them that can be used similarly to hands. The remaining four tentacles each terminate in a single larger spine. While the anime shows that Nihilego can willingly end this merger and it may be disrupted in other ways as well, the lingering toxins and the shock of the separation can leave the host in critical condition, both physically and psychologically.