Initiating a Rush Gauge special attack barrage is the best way to handle it, as the enemy won't die automatically from the attack until it's completed. Some of Arumat's Battle Trophies in Star Ocean: The Last Hope requiring inflicting overkill damage on the foe.Thankfully, party members can't be Overkilled, and in fact enemies will sometimes waste turns hitting a defeated ally. Undead enemies have to be Overkilled otherwise they'll resurrect at the end of the turn (unless the fight ends before then). At that point, they're Overkilled and dissolve into Ether (which you need to cast spells). The DS Glory of Heracles game has defeated enemies hang around on-screen until they take a certain amount of extra damage.

Final Fantasy X has an overkill mechanic if you kill a monster with an attack that exceeds a certain amount of damage, the party will be awarded with more AP and items.This gets added to the automatic coin and sticker reward for winning the battle itself. In Paper Mario: Sticker Star, Paper Mario: Color Splash, and Paper Mario: The Origami King, one extra Heart Point of damage to an enemy beyond its last bit of health becomes one coin.When the level exceeds 200%, you can transform into your Finalized form additionally, ending a battle with upwards of 100% Noise will enable you to obtain Illegal Data. In Mega Man Star Force 3, overkilling an enemy with a non-elemental card attack will increase the Noise level by the amount of extra damage.This is especially true for Deception 4, where the demoness of Sadism will give you bonus ark for doing so. In the Deception series, it always pays to hammer the enemies with as much damage you can dish out in a combo, giving more ark points for designing new traps.

Doing so can also effectively reduce the HP of the final king, as he dies as soon as the combined health bar hits zero. To avoid fighting a 5th king, it's necessary to do extra damage to each king that spawns (or to continue to attack during their rather long death animation).

In a (presumably) unintentional example, the combined health bar of the 4 Kings has slightly more health than those of the individual kings added together.

Enemies drop more souls when one attack does enough damage to One-Hit Kill them (regardless of how much health they had before the last hit).

Bloodborne: As in Dark Souls 1 below, attacking enemies as their death animation plays gives an unintended bonus, only this time it applies to all enemies: you can still regain health from attacking enemies who are in the middle of dying.

Dark souls 3 overkill