Nexus of Destiny

When Nexus of Destiny enters, exile the top five
cards of your library face down. During each
upkeep, a player may pay X, where X is their hand
size, to reveal a random exiled card. If it's a land,
it enters the battlefield; otherwise, they may cast
without paying its mana cost or put a fate counter
on it. Return cards with fate counters to the library instead of the graveyard and draw a card.
If you control five colors, cast an exiled card for
free, then exile Nexus of Destiny.