Rules glossary
↑ Parent rule: 107.3 Many objects use the letter X as a placeholder for a number…
107.3n If a delayed triggered ability created by a resolving spell or ability refers to X, X is not defined in the text of that triggered ability, and the spell or ability that created it had a value of X chosen for any of its costs, the value of X for the triggered ability is the same as the value of X for the spell of ability that created it.
No sub-rules.