Senu, Keen-Eyed Protector

• WOTC Official Reminder Textofficial rules
  Scry — Look at the top N cards of your library, then put any number of them on the bottom of your library and the rest on top in any order.
• WOTC Official Reminder Textofficial rules
  Vigilance — Attacking doesn't cause this creature to tap.

• WWizards of the Coast2024-07-05
  Official Ruling
  Senu's last ability will trigger only if Senu is already exiled at the point immediately after blockers are declared and at least one legendary creature you control that attacked isn't blocked. It's not possible to exile Senu during the declare blockers step in time to have the ability trigger.
• WWizards of the Coast2024-07-05
  Official Ruling
  You choose which player, planeswalker, or battle Senu is attacking when you put it onto the battlefield attacking. It doesn't have to be the same one that the unblocked legendary creature you control is attacking.
• WWizards of the Coast2024-07-05
  Official Ruling
  Although Senu enters the battlefield attacking as a result of its last ability, it was never declared as an attacking creature. Abilities that trigger whenever a creature attacks won't trigger when Senu enters the battlefield attacking.

Rulings via Scryfall