Cheapest priced copy (Dominaria United): $0.35 at Card Kingdom, near mint, their price list as of .
Benalish Sleeper 
Creature — Phyrexian Human Soldier · 3/1 · Common · Dominaria United · #8
Kicker {B} (You may pay an additional {B} as you cast this spell.)
When this creature enters, if it was kicked, each player sacrifices a creature of their choice.
Legal inCommanderPioneerModernLegacyVintagePauper
Not legal inBrawlStandard
1 printing · $0.35 to $0.49 at Card Kingdom
| Set | Number | Rarity | Card Kingdom | Foil |
|---|---|---|---|---|
| Dominaria United | 8 | Common | $0.35 | $0.49 |
8 rulings from Wizards of the Coast
- 9 September 2022As Benalish Sleeper's ability resolves, first the player whose turn it is chooses a creature to sacrifice, then each other player in turn order does the same knowing the choices made before them. Then all those creatures are sacrificed simultaneously.
- 9 September 2022If you kicked it, you may sacrifice Benalish Sleeper itself as its ability resolves. If you control no other creatures, you'll have to sacrifice Benalish Sleeper.
- 8 November 2024If a spell's kicker cost was paid, the spell is "kicked."
- 8 November 2024If you copy a kicked spell on the stack, the copy is also kicked. If the copied spell is a permanent spell, the token the copy of that spell becomes when it enters is also kicked.
- 8 November 2024The kicker ability doesn't let you pay a kicker cost more than once.
- 8 November 2024If you put a permanent with a kicker ability onto the battlefield without casting it, you can't kick it.
- 8 November 2024If a card or token enters as a copy of a permanent, the new permanent isn't kicked, even if the original was.
- 8 November 2024To determine a spell's total cost, start with the mana cost (or an alternative cost if another card's effect allows you to pay one instead), add any cost increases (such as kicker), then apply any cost reductions. The spell's mana value remains unchanged, no matter what the total cost to cast it was.