Johann, Apprentice Sorcerer

If Johann leaves the battlefield and returns to the battlefield in the same turn, or if Johann leaves and another Johann appears, the casting permission granted by the old one is different than the casting permission granted by the new one. On the turn in which the new Johann enters the battlefield, you may use its casting permission once, even if you used the old Johann's casting permission to cast an instant or sorcery spell from the top of your library in that same turn. Note that if you control multiple Johanns you won't have the opportunity to cast an instant or sorcery spell from the top of your library before the "legend rule" gets you down to one Johann.

If the top card of your library has an Adventure, you can cast the Adventure spell this way.

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 a spell from the top of your library, you can't look at the next one until you're done paying for that spell.