Every distinct wording since 2010, newest first.
September 25, 2020 · Zendikar Rising
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.
October 4, 2019 · Throne of Eldraine
Some objects use the letter Y in addition to the letter X. Y follows the same rules as X.