What are the official rulings for Gonti, Lord of Luxury in Magic: The Gathering?

The official rulings for Gonti, Lord of Luxury in Magic: The Gathering state that when Gonti enters the battlefield, you may look at the top four cards of target opponent's library, exile one of them face down, and then put the rest on the bottom of that player's library in a random order. You may cast that exiled card for as long as it remains exiled, and you may spend mana as though it were mana of any type to cast it.