Frilled Deathspitter

• WWizards of the Coast2018-01-19
  Official Ruling
  If multiple sources deal damage to a creature with an enrage ability at the same time, most likely because multiple creatures blocked that creature, the enrage ability triggers only once.
• WWizards of the Coast2018-01-19
  Official Ruling
  If your life total is brought to 0 or less at the same time that Frilled Deathspitter is dealt damage, you lose the game before its enrage ability resolves.
• WWizards of the Coast2018-01-19
  Official Ruling
  If lethal damage is dealt to a creature with an enrage ability, that ability triggers. The creature with that enrage ability leaves the battlefield before that ability resolves, so it won’t be affected by the resolving ability.

Rulings via Scryfall