Cheapest priced copy (Commander Legends: Battle for Baldur's Gate): $5.99 at Card Kingdom, near mint, their price list as of .
Miirym, Sentinel Wyrm 
Legendary Creature — Dragon Spirit · 6/6 · Rare · Secret Lair Drop · #2500
Flying, ward {2}
Whenever another nontoken Dragon you control enters, create a token that's a copy of it, except the token isn't legendary.
Legal inCommanderLegacyVintage
Not legal inBrawlStandardPioneerModernPauper
5 printings · $5.99 to $44.99 at Card Kingdom
| Set | Number | Rarity | Card Kingdom | Foil |
|---|---|---|---|---|
| Commander Legends: Battle for Baldur's Gate | 284 | Rare | $5.99 | $7.99 |
| Commander Legends: Battle for Baldur's Gate | 431 | Rare | $6.49 | $5.99 |
| Commander Legends: Battle for Baldur's Gate | 542 | Rare | — | — |
| Battle for Baldur's Gate Promos | 284s | Rare | — | $15.99 |
| Secret Lair Drop | 2500 | Rare | $42.99 | $44.99 |
2 rulings from Wizards of the Coast
- 10 June 2022If the Dragon that entered the battlefield is copying something else as the triggered ability resolves, the token will be a copy of whatever that creature is a copy of.
- 10 June 2022Miirym, Sentinel Wyrm's triggered ability copies the printed values of the Dragon that entered the battlefield. It won't copy any counters on that creature or any effects that have changed its power, toughness, types, color, and so on.