Rule evolution
Rule 107.3c
Earliest archived Rules release: 2009-10-01 · 0 wording revisions · 0 renumberings
Earliest archived Rules release107.3cDetails
If a spell or activated ability has an {X}, [-X], or X in its cost and/or its text, and the value of X is defined by the text of that spell or ability, then that's the value of X while that spell or ability is on the stack. The controller of that spell or ability doesn't get to choose the value. Note that the value of X may change while that spell or ability is on the stack.