When Stalking Phantom enters, each opponent exiles a card from their hand.

{2}{B}, Exile Stalking Phantom from your graveyard: Extract 1. Activate only as a sorcery. (Exile the top one card of target opponent’s library. If you don’t control a Nightmare token, create a */1 black Nightmare creature token with ‘This creature gets +1/+0 for each creature card your opponents own in exile.’)

1/1