Thoughtbound Phantasm

• WOTC Official Reminder Textofficial rules
  Defender — This creature can't attack.

• WWizards of the Coast2018-10-05
  Official Ruling
  You put only one +1/+1 counter on Thoughtbound Phantasm each time you surveil, no matter how many cards you looked at when you surveilled.
• WWizards of the Coast2018-10-05
  Official Ruling
  Once Thoughtbound Phantasm has attacked, removing +1/+1 counters from it won't remove it from combat.
• WWizards of the Coast2024-01-12
  Official Ruling
  An ability that triggers "whenever you surveil" triggers after you're done surveilling, even if you have fewer cards in your library than the number of cards you're instructed to surveil. It even triggers if you have no cards in your library.

Rulings via Scryfall