With MDFC lands, they can cheat by playing more lands in the deck, and when a Balustrade Spy enters, youll reveal the top card of your library and it will care about the front face of the MDFC
They are Vrondiss, Rage of Ancients (a Dragonborn Barbarian, leading the red/green Draconic Rage deck), Prosper, Tome-Bound (a Tiefling Warlock, helming the red/black Planar Portal deck), Sefris of the Hidden Ways (a Genasi Wizard, leading the White/Blue/Black Dungeons of Death deck), and, finally, Galea, Kindler of Hope (a Half-Elf Paladin, topping the White/Blue/Green Aura of Courage deck)
While he doesn't look blatantly powerful, he can be decently strong when built around properly, like a Faith's RewardFaith's Reward on a stick
Alo said the things to lookout for are