Memory's Shadowstealer

Inspired - Whenever Memory's Shadowstealer
becomes untapped, look at the top five cards of
target player's library, exile up to two of them
face down, then put the rest on the bottom of
that player's library in a random order. For as
long as a card is exiled this way, you may look at
and cast that card. You may spend mana as
though it were mana of any color to cast spells
exiled this way.