When one of the three moons of Neotellus enters into an eclipse, the gateway from the Umbral appears and the Soul Eater will viciously pass through this entrance. Umbral will slice the soul of all his targets using a giant long sword without even making a sound.
Umbral is the adjective form of umbra, meaning "a dark area, especially the blackest part of a shadow from which all light is cut off".
Umbral is one of the few cards in the game whose name changes drastically when evolved. (iOS only)