This enchantment is actually for a map I eventually wanna upload. You can obtain the Overkill Enchantment by combining a dragon head, nether star, echo shard and book in a crafting table. Alternatively, use the command /enchant @s minecraft:overkill or search for overkill in the creative menu.
Usage: Store overkill damage when killing a mob. Overkill damage is equal to the negative value of a mob's HP, if it existed. Overkill damage decreases over time. Hit a mob and deal the stored damage to it.
Equipment: Swords, Axes, Spears, Tridents, Bows, Crossbows and Maces
Ways for these enchantments to work with overkill have been added: Sharpness, Bane of Anthropods, Smite, Power, Impaling and Density. (Warning: Density is a tad inaccurate, but I'd rather be inaccurate in favor of the player)
Balance: Questionable. Open to feedback. In particular, I'm curious if there is a way to have it work accurately with the density enchantment. Feel free to message me under u/Unreasonable_Mess on Reddit.
See debug messages: /tag @s add dev Enable or disable players with high overkill damage glowing: /trigger overkillsetting (This only works if you have the dev tag and reloaded.)
Thanks to: u/TheStarGamer1 (for a smarter approach and getting me motivated to try again) and u/GalSergey (for the crit detection advancement ya posted like 9 months ago)