Cheapest priced copy (The List): $2.99 at Card Kingdom, near mint, their price list as of .
Mirror March 
Enchantment · Rare · Ravnica Allegiance · #108
Whenever a nontoken creature you control enters, flip a coin until you lose a flip. For each flip you won, create a token that's a copy of that creature. Those tokens gain haste. Exile them at the beginning of the next end step.
Legal inCommanderPioneerModernLegacyVintage
Not legal inBrawlStandardPauper
3 printings · $2.99 to $5.99 at Card Kingdom
| Set | Number | Rarity | Card Kingdom | Foil |
|---|---|---|---|---|
| The List | RNA-108 | Rare | $2.99 | — |
| Ravnica Allegiance Promos | 108s | Rare | — | $5.99 |
| Ravnica Allegiance | 108 | Rare | $2.99 | $4.99 |
6 rulings from Wizards of the Coast
- 25 January 2019If the copied creature has {X} in its mana cost, X is 0.
- 25 January 2019Each 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.
- 25 January 2019Any 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.
- 25 January 2019If 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.
- 25 January 2019If the copied creature is copying something else, each token enters the battlefield as whatever that creature is copying.
- 25 January 2019All of the tokens enter the battlefield at the same time.