Parasitic Strix

• WWizards of the Coast2020-08-07
  Official Ruling
  If you don't control a black permanent immediately after Parasitic Strix enters the battlefield, its ability doesn't trigger. If you don't control one as the ability resolves, no player loses or gains life. It doesn't have to be the same black permanent both times, however.
• WWizards of the Coast2020-08-07
  Official Ruling
  Parasitic Strix's ability triggers only once, no matter how many black permanents you control beyond the first.

Rulings via Scryfall