Cheapest priced copy (Commander 2017): $0.59 at Card Kingdom, near mint, their price list as of .
Dark Impostor 
Creature — Vampire Assassin · 2/2 · Rare · Avacyn Restored · #92
{4}{B}{B}: Exile target creature and put a +1/+1 counter on this creature.
This creature has all activated abilities of all creature cards exiled with it.
Legal inCommanderModernLegacyVintage
Not legal inBrawlStandardPioneerPauper
3 printings · $0.59 to $3.49 at Card Kingdom
| Set | Number | Rarity | Card Kingdom | Foil |
|---|---|---|---|---|
| Avacyn Restored | 92 | Rare | $0.69 | $3.49 |
| Commander 2017 | 109 | Rare | $0.59 | — |
| Crimson Vow Commander | 127 | Rare | $0.59 | — |
6 rulings from Wizards of the Coast
- 1 May 2012If an activated ability of a card in exile references the card it's printed on by name, treat Dark Impostor's version of that ability as though it referenced Dark Impostor by name instead. For example, if Marrow Bats (which says "Pay 4 life: Regenerate Marrow Bats") is exiled with Dark Impostor, Dark Impostor has the ability "Pay 4 life: Regenerate Dark Impostor."
- 1 May 2012Once Dark Impostor leaves the battlefield, it will no longer have the activated abilities of the creature cards exiled with it. If it returns to the battlefield, it will be a new Dark Impostor with no connection to those exiled cards.
- 1 May 2012Dark Impostor gains only activated abilities. It doesn't gain triggered abilities or static abilities. Activated abilities contain a colon. They're generally written "[Cost]: [Effect]." Some keywords are activated abilities; they have colons in their reminder text.
- 1 May 2012Dark Impostor can target and exile a permanent that's only a creature temporarily, like an animated land. However, because that card isn't a creature card, Dark Impostor won't have any of that card's activated abilities.
- 1 May 2012If you control more than one Dark Impostor, each will have only the activated abilities of creature cards exiled with that specific Dark Impostor.
- 24 September 2021If Dark Imposter exiles a double-faced card, it will only have activated abilities of the front face of that exiled card, no matter which face was up on the battlefield.