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)
Manifesting a card puts it onto the battlefield as a 2/2 creature, and you can turn it face-up by paying its mana cost
Fetch Lands Mana fixing alone is far from broken, but fetch lands do so much more
If Explorer's Cache isn't on the battlefield as its activated ability resolves, you can't remove a +1/+1 counter from it, so you won't put a +1/+1 counter on the target creature
A card I considered but ultimately removed from this list was another Ral Zarek card, Blast of Genius
It is not an EX card, so you do not have to worry about your opponent gaining two points when it is defeated