2016-08-23 : If there is an {X} in the mana cost of the exiled creature card, that X is 0. Don’t confuse it with the {X} in the activation cost of Caller of the Untamed’s ability.

2016-08-23 : 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.