Whenever an opponent casts a spell, reveal the top card of your library. If it’s a creature card, put it onto the battlefield. Otherwise, you may put that card on the bottom of your library.
A "creature card" is any card with the type creature, even if it has other types such as artifact, enchantment, or land. Older cards of type summon are also creature cards.
01-10-2009
wotc
If an opponent casts a spell, this ability triggers and is put on the stack on top of that spell. This ability will resolve (meaning that a revealed creature card will enter) before the spell resolves.
01-10-2009
wotc
You must put the revealed card onto the battlefield if it's a creature card. If it's not a creature card and you don't put it on the bottom of your library, it stops being revealed and simply remains on top of your library.
Random a card of Magic: The Gathering (MTG), but you can also roll the D20 dice, random a Planeswalker, have fun with the random rules and more.