Innercity Markethall

When Innercity Markethall enters the battlefield,
discard the three top cards of your library,
put a 1/1 black and white sentinel creature token
onto the battlefield for each non-land permanent discarded this way.
{t}: Add {w}, {u} or, {b} to your mana pool.
{w/b}, {t}: Exile the top card of your graveyard