Duncan, Who Borrows Decks

Constellation — Whenever Duncan, Who Borrows Decks or another enchantment
enters the battlefield under your control,
Pick a player at random. Exile the top card of that player's library face down. If the face
down card is white, reveal it and repeat this effect. You may cast cards exiled this way as
if they were in your hand, and you may pay
mana as if it were any color to do so.