The Necromorphs in the DeadSpace trilogy are a interesting and damn deadly combination of ideas. Essentially they are space zombies brought on by on an ancient alien marker. The victims go violently insane and once dead their bodies are reconfigured into ghoulish malformations. The only way to destroy them is by completely dismembering them. These stand out because of how freakish and original there attacks are and how easily they can swarm you in the enclosure of space. May the gaming gods bring you glory.