Thromian the Dishonored

When Thromian the Dishonored enters the battlefield, if you cast it from your hand look at
the top five cards of your library. You may reveal
a Shark creature from among them and put it
onto the battlefield. If you do, return Thromian
the Dishonored to its owner's hand. Then put
any number of the remaining cards on top of
your library in any order and the rest on the
bottom of your library in any order.