Cheapest priced copy (Dominaria United Commander): $1.79 at Card Kingdom, near mint, their price list as of .
Activated Sleeper 
Creature — Phyrexian Shapeshifter · 0/0 · Rare · Dominaria United Commander · #24
Flash
You may have this creature enter as a copy of any creature card in a graveyard that was put there from the battlefield this turn, except it's a Phyrexian in addition to its other types.
Legal inCommanderLegacyVintage
Not legal inBrawlStandardPioneerModernPauper
2 printings · $1.79 to $2.99 at Card Kingdom
| Set | Number | Rarity | Card Kingdom | Foil |
|---|---|---|---|---|
| Dominaria United Commander | 24 | Rare | $1.79 | $2.99 |
| Dominaria United Commander | 74 | Rare | $2.49 | $1.99 |
3 rulings from Wizards of the Coast
- 9 September 2022You don't have to choose a card to copy. If you don't, Activated Sleeper enters the battlefield as a 0/0 creature and is probably put into your graveyard immediately, unless something is increasing its toughness to keep it alive.
- 9 September 2022If the chosen creature card has {X} in its mana cost, X is considered to be zero.
- 9 September 2022Treat Activated Sleeper as though it were the chosen card entering the battlefield, except it's also a Phyrexian. Any "As [this creature] enters the battlefield," "[This creature] enters the battlefield with," and "When [this creature] enters the battlefield" abilities of the chosen card will work.