Heimerdinger, Reverie Creator

When Heimerdinger, Reverie Creator enters the battlefield, look at the top 3 cards of your library.
You may put any number of them onto the battlefield face-down as 1/1 artifact creatures.
Turn them face up for their mana cost at any
time you could cast them if they are instant or
sorcery cards.
Whenever you turn an instant or sorcery card
face up, you may cast it without paying its mana
cost.