Cheapest priced copy (Kaldheim): $5.99 at Card Kingdom, near mint, their price list as of .
Kaya the Inexorable 
Legendary Planeswalker — Kaya · Mythic · Kaldheim · #218
+1: Put a ghostform counter on up to one target nontoken creature. It gains "When this creature dies or is put into exile, return it to its owner's hand and create a 1/1 white Spirit creature token with flying."
−3: Exile target nonland permanent.
−7: You get an emblem with "At the beginning of your upkeep, you may cast a legendary spell from your hand, from your graveyard, or from among cards you own in exile without paying its mana cost."
Legal inCommanderPioneerModernLegacyVintage
Not legal inBrawlStandardPauper
5 printings · $5.99 to $15.99 at Card Kingdom
| Set | Number | Rarity | Card Kingdom | Foil |
|---|---|---|---|---|
| Kaldheim | 218 | Mythic | $5.99 | $5.99 |
| Kaldheim | 288 | Mythic | $5.99 | $8.99 |
| Kaldheim Promos | 218p | Mythic | $9.99 | $11.99 |
| Kaldheim Promos | 218s | Mythic | — | $15.99 |
| Planeswalker Championship Promos | 2021-5 | Mythic | — | — |
5 rulings from Wizards of the Coast
- 5 February 2021If the spell has {X} in its mana cost, you must choose 0 as the value of X.
- 5 February 2021If you cast a spell “without paying its mana cost,” you can’t choose to cast it for any alternative costs. You can, however, pay additional costs, such as kicker costs. If the card has any mandatory additional costs, those must be paid to cast the spell.
- 5 February 2021If you own a face-down card in exile, Kaya’s emblem will let you cast it only if you can look at the card (and only if it’s legendary). If you aren’t allowed to look at the card, you can’t cast it, even if you know it’s legendary.
- 5 February 2021The ghostform counter added by the first ability doesn’t have any functional importance. It’s there to remind you of the ability the creature gains. Even if that counter is removed from the creature, the triggered ability it gains will still work.
- 5 February 2021If a nontoken creature gains more than one instance of that triggered ability, each of them will trigger separately. You can return the card to its owner’s hand only once, but you’ll create a Spirit creature token for each of those abilities.