Priest of Titania

• WWizards of the Coast2024-06-07
  Official Ruling
  Priest of Titania's ability counts all Elves on the battlefield. This includes Priest of Titania itself as well as Elves controlled by other players.
• WWizards of the Coast2024-06-07
  Official Ruling
  Priest of Titania's ability is a mana ability. It doesn't use the stack and players can't respond to it. Notably, this means other players can't try to remove Elves from the battlefield after you activate this ability but before it resolves.

Rulings via Scryfall