There are two blows I narrate as significant, The one that introduced (in 4e) a bloodied condition, and that would usually be a minor scrap, cut or crush, and the blow that drops the monster, which could be significant or not, depending on whether it dropped it to over -10, or just below 0.
Monsters on 0HP drop, but don't die, in my campaigns.
Monsters on 0HP drop, but don't die, in my campaigns.