Ok, so this question has to do with Type 4, which is a casual format where players play off the same giant deck. The deck is split into about 8 libraries. Each player has unlimited mana, but can only cast one spell per turn. Sometimes a card will allow a player to play extra spells, like the following card:
Josh Coyne, Future Seer5UUU
Planeswalker - Josh
Play with the top card of each library revealed.
+3: Choose a color. Draw each revealed card of that color.
-6: Choose a card type. Cast any number of revealed cards of that type.
Loyalty: 6
Suppose Josh's controller, who I'll call John, activates the -6 ability and names creature. There are two creatures on top of libraries. John casts the first creature. Does the next card get revealed now or after both creatures are cast? If the next card is revealed now, and it's a creature, can John cast it as well?
Similarly, with the +3 ability, if John chooses blue and there are three blue cards revealed, does he reveal the next card after the first draw or not until he has drawn all 3 cards? If he reveals a blue card this way, can he draw that as well?
I found this on Gatherer, regarding Oracle of Mul Daya. Maybe it applies here:
4/15/2013
If the top card of your library changes while you’re casting a spell, playing a land, or activating an ability, the new top card won’t be revealed until you finish doing so.
I've never heard of Type 4 until just now. Fortunately, your question doesn't actually have anything to do with the format. For the theoretical ability mentioned on Josh Coyne, Future Seer, with only the top card of your library revealed you could only cast the top card of your library because during the resolution of an ability the top card of your library effectively doesn't change. As you found with Oracle, during the action of activating or casting the top card doesn't change even if you are casting the top card of your library. Which is to say you declare you are casting the top card of your library. It moves to the stack but you don't see the new top card until you finish the entire process of casting. This is partially to prevent legal cheating by casting the top of your library when you couldn't to see what was next.
Thank you user_938036! I have a follow up question. I saw the following ruling concerning Oracle of Mul Daya:
4/15/2013 When playing with the top card of your library revealed, if an effect tells you to draw several cards, reveal each one before you draw it.
Doesn't that contradict the first ruling? I'll paste the first ruling here for reference:
4/15/2013 If the top card of your library changes while you’re casting a spell, playing a land, or activating an ability, the new top card won’t be revealed until you finish doing so.
Thank you user_938036! I have a follow up question. I saw the following ruling concerning Oracle of Mul Daya:
4/15/2013 When playing with the top card of your library revealed, if an effect tells you to draw several cards, reveal each one before you draw it.
Doesn't that contradict the first ruling? I'll paste the first ruling here for reference:
4/15/2013 If the top card of your library changes while you’re casting a spell, playing a land, or activating an ability, the new top card won’t be revealed until you finish doing so.
Sorry it took so long to get back, didn't see an update on the rulings despite frequenting CCC.
It's not contradictory because they aren't at all the same thing. One is handling the revealing of the top of your library while something is casting/activating. The other is specifically handling revealing cards as you draw them. Because card draws can happen as part of a cost, part of an effect resolving or as part of a turn action it gets its own rules to handle so they are treated differently from similar but different events.
Josh Coyne, Future Seer 5UUU
Planeswalker - Josh
Play with the top card of each library revealed.
+3: Choose a color. Draw each revealed card of that color.
-6: Choose a card type. Cast any number of revealed cards of that type.
Loyalty: 6
Suppose Josh's controller, who I'll call John, activates the -6 ability and names creature. There are two creatures on top of libraries. John casts the first creature. Does the next card get revealed now or after both creatures are cast? If the next card is revealed now, and it's a creature, can John cast it as well?
Similarly, with the +3 ability, if John chooses blue and there are three blue cards revealed, does he reveal the next card after the first draw or not until he has drawn all 3 cards? If he reveals a blue card this way, can he draw that as well?
Thank you so much for your help!
4/15/2013
If the top card of your library changes while you’re casting a spell, playing a land, or activating an ability, the new top card won’t be revealed until you finish doing so.
4/15/2013 When playing with the top card of your library revealed, if an effect tells you to draw several cards, reveal each one before you draw it.
Doesn't that contradict the first ruling? I'll paste the first ruling here for reference:
4/15/2013 If the top card of your library changes while you’re casting a spell, playing a land, or activating an ability, the new top card won’t be revealed until you finish doing so.
It's not contradictory because they aren't at all the same thing. One is handling the revealing of the top of your library while something is casting/activating. The other is specifically handling revealing cards as you draw them. Because card draws can happen as part of a cost, part of an effect resolving or as part of a turn action it gets its own rules to handle so they are treated differently from similar but different events.