Gonti, Lord of Luxury

You may look at and cast that card (and spend mana as though it were mana of any type to do so) even if Gonti leaves the battlefield. If another player gains control of Gonti, that player can't look at or cast the card, and you still can.

Gonti doesn't change when you can cast the exiled card. For example, if you exile a creature card without flash, you can cast it only during your main phase when the stack is empty.

An effect that instructs you to "cast" a card doesn't allow you to play lands.