Bellowing Aegisaur

• WWizards of the Coast2017-09-29
  Official Ruling
  If another creature you control is dealt lethal damage at the same time that Bellowing Aegisaur is dealt damage, the other creature won't be saved by the +1/+1 counter that would have been put on it.
• 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