Starseer Mentor

• WOTC Official Reminder Textofficial rules
  Vigilance — Attacking doesn't cause this creature to tap.

• WWizards of the Coast2024-07-26
  Official Ruling
  While resolving Starseer Mentor’s last ability, the target opponent chooses a card to be discarded without revealing it, chooses a nonland permanent to be sacrificed, or chooses to do neither. Then that player discards that card, sacrifices that permanent, or loses 3 life. That player can always choose to lose 3 life, even if they have cards to discard or nonland permanents to sacrifice.
• WWizards of the Coast2024-07-26
  Official Ruling
  Starseer Mentor’s ability cares whether you gained or lost life this turn, not how your life total changed. For example, if you gained 2 life and lost 2 life in the same turn, you still gained and lost life that turn, even though your life total is the same as it was at the start of the turn.

Rulings via Scryfall