Codie, Ravenous Codex

A preparation card is a creature card in every zone. For example, while it's in your graveyard, Diviner of Victory is a blue creature card whose mana value is 1. It can't be the target of Stingcaster Mage's triggered ability ("When this creature enters, target instant or sorcery card in your graveyard gains flashback until end of turn. The flashback cost is equal to its mana cost.").

If an effect instructs you to choose a card name, you may choose the alternative prepare spell's name. Consider only the alternative characteristics to determine whether that is an appropriate name to choose.

A creature with a prepare spell can't become prepared more than once at the same time. For example, say Bloodline Recollector is on the battlefield and is prepared. During the current turn, three creatures die. At the beginning of the end step, Bloodline Recollector's last ability triggers. When that ability resolves, since Bloodline Recollector is already prepared, the ability won't cause it to become prepared a second time or create a second copy of Ancestral Craving in exile.

Only the current controller of a prepared creature can cast the copy of its prepare spell in exile. It doesn't matter who owns that creature or who controlled it when it became prepared.

While copies of spells in zones other than the stack cease to exist when state-based actions are checked, this does not apply to copies of prepare spells in exile that were created as a creature became prepared.

If a prepared creature stops being a creature, it will still be prepared, and the copy of its prepare spell will remain in exile. That permanent's controller will still be able to cast it. The same is true if a prepared creature becomes a copy of something else, even if it's then a permanent without a prepare spell.