Rules glossary
↑ Parent rule: 107.3 Many objects use the letter X as a placeholder for a number…
107.3m If an object’s enters-the-battlefield triggered ability or replacement effect refers to X, and the spell that became that object as it resolved had a value of X chosen for any of its costs, the value of X for that ability is the same as the value of X for that spell, although the value of X for that permanent is 0. This is an exception to rule 107.3i.
No sub-rules.