Technically, yes it's real.
However do not, this Arceus type can ONLY BE OBTAINED BY HACKING
Also mention that it only works in Gen 4. ??? type itself doesn't exist from Gen 5 and onward, and Arceus wasn't in Gens 2 and 3.
commented 5 minutes ago by ƒιzz
Thanks Fizz o3o
Arceus has the Ability Multitype, which changes its type and appearance depending on the Plate it is holding. Likely as a precaution for Arceus hacked to be ???-type, a ???-type sprite of Arceus is present in Diamond, Pearl, Platinum, HeartGold, and SoulSilver Versions; however, it is never used without hacking. It is also likely that this ???-type Arceus was made so that Arceus wouldn't crash the game whenever it tried using Multitype to change its type, although this is probably not the case due to the lack of a ???-type Kecleon.
What it looks like;
However THERE IS NO PLATE.
while there exists a ???-type Arceus in the Generation IV data, there is no associated ??? Plate,