Moved from Recipes+, made by Danto_119 (me), to be a datapack on it's own
The datapack does not work if the world was created straight to creative, to use it on a creative map, start in survival with cheats on and set the gamemode to creative afterwards
The datapack is made for all neutral and hostile mobs (working on it)
Later, add for passive mobs
And other ideas I may come up with

Changed moster_slayer subfolder to hostile, neutral and passive
Absolute Salyer title for skeletons and zombies types
Butcher title for farm animals

05/10/2025
Remade the ones from my original file, next target is to set the 1000 kills ("Slayer Title") for all mobs, so the scoreboard would exist and may be partially seen, so I may post the datapack partially functionable as I wish.
Icon for all first kills to be the spawn egg

All hostile mobs have "Kill" and "Slayer" advancement, and all mobs have a scoreboard created

06/10/2025
Added "Enderman Kill!" and "Spider Kill!"
"root" created for neutral mobs, not all neutral mobs will be there, some will still be on the "hostile" page
All neutral mobs have "the first kill" advancement, removed the dublicate of "trader_llama"