Mirror March

• WWizards of the Coast2019-01-25
  Official Ruling
  If the copied creature has in its mana cost, X is 0.
• WWizards of the Coast2019-01-25
  Official Ruling
  Each token copies exactly what is printed on the creature and nothing else (unless that creature is copying something else; see below). It doesn’t copy whether that creature is tapped or untapped, whether it has any counters on it or Auras and/or Equipment attached to it, or any non-copy effects that changed its power, toughness, types, color, and so on.
• WWizards of the Coast2019-01-25
  Official Ruling
  Any enters-the-battlefield abilities of the copied creature will trigger when the token enters the battlefield. Any “As [this creature] enters the battlefield” or “[This creature] enters the battlefield with” abilities of the copied creature will also work.
• WWizards of the Coast2019-01-25
  Official Ruling
  If the entering creature leaves the battlefield before Mirror March’s ability resolves, use that creature’s last known existence on the battlefield to determine the token’s characteristics.
• WWizards of the Coast2019-01-25
  Official Ruling
  If the copied creature is copying something else, each token enters the battlefield as whatever that creature is copying.
• WWizards of the Coast2019-01-25
  Official Ruling
  All of the tokens enter the battlefield at the same time.

Rulings via Scryfall