Just a step up from the false ones, likely as a once per day challenge and only available after beating every FG.
They would have 150 card decks (approx) and draw 3 cards per turn. Each card within the deck would be a blank card that the AI could use as any card of its choice. Each opponent would have a set card pool to choose from though, so as to make them all different.
Their starting health would be 300 and they would not experience limits on maximum HP gain like players.
They would have either 5x mark for mono decks or 2x "Mark of Divinity" for non-monos. This new mark would act like an unupped Nova every turn and yes, it probably would look like Zanzarino's avatar.
These decks are not expected to be beatable. It must be made to be nigh impossible to defeat them for their name to hold any meaning. Otherwise they are just another level of farming, rather than the ultimate challenge that they are meant as.