How Is This a Par Three?! is not legal in any format.
Rulings
2022-10-07
If X is greater than the number of cards in the targeted player's library, you can't choose to have them mill any cards. This is because if you are given a choice and one of the options is impossible, you can't choose the impossible option. (That means you should make sure to cast Our Market Research Shows That Players Like Really Long Card Names So We Made this Card to Have the Absolute Longest Card Name Ever Elemental before their library gets too small.)