When you copy an activated ability you copy the effect, that is everything after the colon. You don't copy the cost. Any part of the effect based on the cost will remember how the cost was paid for the original activation. That is, you will only pay the cost once and copy the card twice, being able to cast both copies.
May 13, 2018 12:57 p.m.
So even if I used Kaho, Minamo Historian, the original spell chosen would be cast twice instead of a new spell choice?
May 13, 2018 2:20 p.m.
No. You choose the spell to cast as Kaho, Minamo Historian's ability resolves. When the copy resolves you can choose the X costed spell you wanted and cast it. When the original resolves the spell you wanted will no longer be there, you will have cast it and it is most likely now in your graveyard. If there is another exiled spell with the same converted mana cost you will be able to choose to cast that, but remember it has to have the same converted mana cost, you won't be able to choose a cheaper one.