Cheapest priced copy (Final Fantasy Commander): $0.49 at Card Kingdom, near mint, their price list as of .
Yuna's Whistle 
Instant · Rare · Final Fantasy Commander · #75
Reveal cards from the top of your library until you reveal a creature card. Put that card into your hand and the rest on the bottom of your library in a random order. When you reveal a creature card this way, put X +1/+1 counters on target creature you control, where X is the mana value of that card.
Legal inCommanderLegacyVintage
Not legal inBrawlStandardPioneerModernPauper
2 printings · $0.49 to $0.79 at Card Kingdom
| Set | Number | Rarity | Card Kingdom | Foil |
|---|---|---|---|---|
| Final Fantasy Commander | 75 | Rare | $0.49 | $0.49 |
| Final Fantasy Commander | 126 | Rare | $0.79 | $0.79 |
2 rulings from Wizards of the Coast
- 6 June 2025You don't choose a target for Yuna's Whistle at the time you cast it. Rather, a second "reflexive" ability triggers when you reveal a creature card this way. You choose a target for that ability as it goes on the stack. Each player may respond to this triggered ability as normal.
- 6 June 2025If the revealed card has {X} in its mana cost, X is 0 for the purpose of determining its mana value.