Overgrown Armasaur

• 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.
• 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.

Rulings via Scryfall