Cheapest priced copy (Modern Horizons 3 Commander): $0.49 at Card Kingdom, near mint, their price list as of .
Skyclave Apparition 
Creature — Kor Spirit · 2/2 · Rare · Bloomburrow Commander · #154
When this creature enters, exile up to one target nonland, nontoken permanent you don't control with mana value 4 or less.
When this creature leaves the battlefield, the exiled card's owner creates an X/X blue Illusion creature token, where X is the mana value of the exiled card.
Legal inCommanderPioneerModernLegacyVintage
Not legal inBrawlStandardPauper
10 printings · $0.49 to $10.99 at Card Kingdom
| Set | Number | Rarity | Card Kingdom | Foil |
|---|---|---|---|---|
| Bloomburrow Commander | 154 | Rare | $0.59 | — |
| Game Day Promos | 2 | Rare | — | $10.99 |
| Modern Horizons 3 Commander | 172 | Rare | $0.49 | $0.99 |
| Mystery Booster 2 | 18 | Rare | $0.59 | — |
| The List | BLC-154 | Rare | — | — |
| Zendikar Rising Promos | 39p | Rare | $0.49 | $1.49 |
| Zendikar Rising Promos | 39s | Rare | — | $2.79 |
| Secrets of Strixhaven Commander | 173 | Rare | $0.69 | — |
| Zendikar Rising | 39 | Rare | $0.59 | $0.79 |
| Zendikar Rising | 322 | Rare | $1.99 | $4.99 |
4 rulings from Wizards of the Coast
- 25 September 2020If a creature on the battlefield has {X} in its mana cost, X is considered to be 0.
- 25 September 2020If Skyclave Apparition's first ability exiled more than one card owned by a single player, that player creates a token with power and toughness equal to the sum of those cards' mana values. If the first ability exiled cards owned by more than one player, each of those players creates a token with power and toughness equal to the sum of the mana values of all cards exiled by the first ability.
- 25 September 2020If Skyclave Apparition leaves the battlefield before its first ability resolves, the ability still exiles the target permanent.
- 25 September 2020If there's no exiled card when Skyclave Apparition leaves the battlefield (most likely because its first ability hasn't resolved yet), no player creates a token.