The Nyx was an experimental biological weapon developed by Umbrella which appeared in Resident Evil Outbreak: File #2. This abomination appeared to be an amorphous mass of fleshy tendrils and was capable of absorbing organic matter on contact, increasing its mass and power.
During the Raccoon City Destruction Incident in 1998, the Nyx was stolen by a renegade squad of Umbrella Special Service operatives acting under orders from a rogue Umbrella researcher. The retrieval of the Nyx's storage capsule did not go as planned and the monster was inadvertently released on the highway where it attacked and consumed an entire squad of UBCS mercenaries. It later fought against a Tyrant and assimilated it too. Powerful though it was, the Nyx was not invincible and a determined group of survivors were able to destroy the creature.