Wasn't he given 3.X-era stats when they released the show on DVD?
Apparently that had him as a Male half-fiend human sorcerer 13/archmage 5, NE medium outside (native). CR 21.
In the cartoon, do we actually ever see Venger *do* enough personally to give him stats? My (admittedly) vague memory is that he's more a motive presence for the plot than something the PCs interact with in any combat rules sense.
Might make more sense as a Warlock now. He did seem to spam a lot of Eldritch Bolt style attacks.
And that dude has GOT to have some friggin evil patron he pays homage to....