If you have more than one Caller of the Untamed in your deck, you may reveal any number of them and exile that many creature cards you drafted that aren’t in your deck. You’ll choose which one to copy at the time you choose the value of X while activating the ability.

If there is an in the mana cost of the exiled creature card, that X is 0. Don’t confuse it with the in the activation cost of Caller of the Untamed’s ability.