Rule 722.3c

As a permanent with a prepare spell gains the prepared designation or phases in prepared, its controller creates a copy of that object in exile, except that copy has only the characteristics of that permanent’s prepare spell, ignoring other exceptions to the copying process that apply to that permanent. Those characteristics become the copy’s normal characteristics. This copy remains in exile for as long as the prepared permanent remains on the battlefield and has the prepared designation. This is an exception to rule 704.5e. For as long as the copy remains in exile, the prepared permanent’s controller may cast the copy. That permanent loses the prepared designation at the time the spell becomes cast (see rule 601.2i). Example: A player casts Croaking Counterpart targeting an Encouraging Aviator. Croaking Counterpart is an instant that says, in part, “Create a token that’s a copy of target non-Frog creature, except it’s a 1/1 green Frog.” Encouraging Aviator is a preparation creature card which says, in part, “Whenever this creature attacks, it becomes prepared.” Its prepare spell is an instant named Jump which says “Target creature gains flying until end of turn.” The player then attacks with the token copy of Encouraging Aviator. As the token copy of Encouraging Aviator becomes prepared, the copy created in exile is a blue instant named Jump that says “Target creature gains flying until end of turn.” It is not green, nor does it have power and toughness 1/1 or the Frog creature type.