Vitium is a mysterious creature that first appeared in Digimon World Re:Digitize, and so far, nothing much is known about it so far. The Grand One is currently undergoing experiments with Vitium, seeing what the heck it even is, but so far results are inconclusive as of 7/30/2012. Like Artilimon, it's name stays the same regardless of the stage, but it is currently unknown if Vitium is a Digimon or not, or if it's a creature along the lines of the D-Reaper.
Vitium first appeared in Digimon World Re:Digitize, but hardly anything is known about it. It came to life in the B/C universe when it was first discovered in another universe, a parallel world of the Adventure Universe as the famous File Island was present, and even some of the famous Adventure cast was present. It is unknown if they ever saw Vitium for themselves, however, leaving any possible information in the dark as to what it could possibly be. Not even Dragoramon can tell what it is, but says that Vitium is extremely powerful even in it's Rookie stage, that is, if it's first form even is a Rookie Level and it is a Digimon at all...
Digimon World: Bronze and Cobalt Versions
Vitium is obtained when it's currently unknown final form is beaten in a bonus quest, unlocked by a password much like Fracktamon and Goddreamon's quests. However, while all the other password quests give you the specific Digimon's exact location, Vitium must be found with the ONLY hint being given is that it is located on B/C's version of File Island, which was supposed to be long since desolate after being frozen over by ice thousands of years ago. Vitium becomes it's Champion Level equivalent when it reaches Level 30 with 10,000 Machine Exp.