Srsly, though.
Even Nix "SuperJudge" Uotan was unable to comprehend 'meta' powers like that, as seen when the Gentry manipulated the comic book panels around him during Multiversity.
So couple that with Mordru's ability to casually stuff universal energies into the gem, and then discard it like it's still some low-level trinket that isn't even worth his time, and you begin to start understanding the levels of power he's packing here.
And bear in mind that everything Zatanna and Dianna do from here can be directly related to the power that Mordru lent them.