Galvanoth

Oracle Text

At the beginning of your upkeep, you may look at the top card of your library. If it's an instant or sorcery card, you may cast it without paying its mana cost.

Card Rulings

6/1/2011 If the card you look at isn’t an instant or sorcery card, it remains on top of your library. You don’t reveal it.
6/1/2011 You may pay additional costs, such as kicker costs, of the instant or sorcery card.
6/1/2011 If the card has any mandatory additional costs, as Kuldotha Rebirth does, you must pay them in order to cast the spell.
6/1/2011 If the card has an X in its mana cost, you must choose 0 as its value.