Omnipresent Impostor is a rare Basic Creature — Shapeshifter card from Mystery Booster 2 (MB2), collector number 504. Current market price: $0.43, TCGplayer market prices via Scryfall.
Changeling Omnipresent Impostor has all card names. As you search your library for one or more cards, you may choose Omnipresent Impostor as one of those cards. (For example, if you search for two land cards, you may find Omnipresent Impostor and a land card.)