Carnivorous Cultivator // Enroot

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.

Casting a copy of a prepare spell from exile isn't casting it for an alternative cost. Effects that allow you to cast a spell for an alternative cost or without paying its mana cost may allow you to apply those to a copy of a prepare spell cast from 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.