If a cost associated with a special action, such as a suspend cost or a morph cost, has an {X} or an X in it, the value of X is chosen by the player taking the special action immediately before they pay that cost.
April 27, 2018 · Dominaria
If a cost associated with a special action, such as a suspend cost or a morph cost, has an {X} or an X in it, the value of X is chosen by the player taking the special action as they pay that cost.
September 30, 2011 · Innistrad
If a cost associated with a special action, such as a suspend cost or a morph cost, has an {X} or an X in it, the value of X is chosen by the player taking the special action as he or she pays that cost.
June 17, 2011 · Commander 2011
If a cost associated with a special action, such as a suspend cost or a morph cost, has an {X}
February 4, 2011 · Mirrodin Besieged
If a cost associated with a special action, such as a suspend cost or a morph cost, has an {X} or an X in it, the value of X is chosen by the player taking the special action as he or she pays that cost.
October 1, 2010 · Scars of Mirrodin
If a cost associated with a special action, such as a suspend cost or a morph cost, has an {X}
February 1, 2010 · Worldwake
If a cost associated with a special action, such as a suspend cost or a morph cost, has an {X} or an X in it, the value of X is chosen by the player taking the special action as he or she pays that cost.