Vizier of the Menagerie

You'll still pay all costs for that spell, including additional costs. You may also pay alternative costs such as emerge or that of As Foretold.

If the top card of your library changes while you're casting a spell, playing a land, or activating an ability, you can't look at the new top card until you finish doing so. This means that if you cast the top card of your library, you can't look at the next one until you're done paying for that spell.

You may spend mana as though it were mana of any type to cast any creature spell, not just creature spells that you cast from the top of your library.