The ability is put on the stack immediately after you cast a creature spell, which means the creature that spell will become won't be a legal target.
01-08-2008
wotc
The ability will still resolve even if the spell that triggered it gets countered.
01-04-2008
wotc
A "creature spell" is any spell with the type Creature, even if it has other types such as Artifact or Enchantment. Older cards of type Summon are also Creature spells.
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.