So recently my D&D group decided to have a between-players tournament. The first battle was the party cleric, Athuriel, versus the paladin Galain. 

Athuriel was at 23 HP, Galain at 24. Athie cast Guiding Bolt, and got a nat-20.

But see

The thing is

Galain has an item called the Ring of Retribution. What it does is, when an attacker scores a critical hit on the user, the attacker takes however much damage they deal.

Athie’s attack dealt 23 damage. 

She literally dealt the exact amount of damage needed to knock her to 0 HP.

It was so fantastic, I couldn’t stop cackling