Treasure Keeper

If you cast a spell "without paying its mana cost," you can't choose to cast it for any alternative costs. You can, however, pay additional costs. If the card has any mandatory additional costs, those must be paid to cast the spell.

If your library has no nonland cards in it with mana value 3 or less, you'll reveal all the cards in your library, then put them back in a random order.

If you don't cast the nonland card with mana value 3 or less, it'll be put on the bottom of your library in a random order with the other cards.