The Stheno is a large variant of Napad, a Complete Mutation derived from C-Virus-infected humans known as J'avo. Its name is derived from the Greek Σθεννώ, a Gorgon in mythology.
Stheno only appears in Resident Evil: Revelations 2's Raid Mode as part of the Huge Creatures online event. The Stheno is a "Huge Creature", that walks slowly towards the player avatars, alongside the Medusa and the Euryale. The damage inflicted on the creature's enormous HP is accumulated through all the online players damage, making defeating them a cooperative effort between all Raid Mode players.