Ulamog's Rebuilder

When Ulamog's Rebuilder enters the battlefield,
if you cast it, each player exiles the top 20 cards
of their library.
{t}, Put 5 cards in exile into their owner's
graveyards: Add {c}{c}, then search your library
for up to two wastes and put them onto the battlefield.
{5}{t}: Choose a card in exile. You may cast or
play it as if it had flash for the rest of the game.