Flumph

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

• WWizards of the Coast2021-07-23
  Official Ruling
  Flumph's ability will trigger even if it is dealt lethal damage.
• WWizards of the Coast2021-07-23
  Official Ruling
  If the opponent is somehow an illegal target for Flumph's ability when it tries to resolve, neither player will draw a card.
• WWizards of the Coast2021-07-23
  Official Ruling
  Flumph's triggered ability is not optional. You must target an opponent if able.
• WWizards of the Coast2021-07-23
  Official Ruling
  Flumph's ability only triggers once each time it is dealt damage, even if multiple sources are dealing damage to it at once.

Rulings via Scryfall