Cheapest priced copy (Commander 2021): $0.49 at Card Kingdom, near mint, their price list as of .
Stalking Leonin 
Creature — Cat Archer · 3/3 · Rare · Murders at Karlov Manor Commander · #86
When this creature enters, secretly choose an opponent.
Reveal the player you chose: Exile target creature that's attacking you if it's controlled by the chosen player. Activate only once.
Legal inCommanderLegacyVintage
Not legal inBrawlStandardPioneerModernPauper
4 printings · $0.49 to $0.79 at Card Kingdom
| Set | Number | Rarity | Card Kingdom | Foil |
|---|---|---|---|---|
| Commander 2017 | 7 | Rare | $0.79 | — |
| Commander 2021 | 105 | Rare | $0.49 | — |
| Murders at Karlov Manor Commander | 86 | Rare | $0.49 | — |
| The List | C17-7 | Rare | $0.49 | — |
5 rulings from Wizards of the Coast
- 25 August 2017If you didn't choose an opponent when Stalking Leonin entered the battlefield, you can't pay the cost to activate its last ability. This will usually happen because you gained control of another player's Stalking Leonin or because a creature already on the battlefield became a copy of Stalking Leonin.
- 25 August 2017If you have multiple Stalking Leonins, you may choose a different opponent for each one. Be careful to keep track of which opponent is chosen for each Stalking Leonin.
- 25 August 2017There are several ways to secretly choose an opponent, including writing that player's name on a piece of paper that's kept with Stalking Leonin.
- 25 August 2017If Stalking Leonin leaves the battlefield and returns, it's considered a new object. You may choose a new opponent and you may activate its last ability again.
- 25 August 2017If a creature is attacking a planeswalker you control, it's not attacking you. Stalking Leonin's last ability can't target it.