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

Version 1.0.1
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"

Version 1.0.2
07/10/2025
Solved "creeper" not showing on achievements tab
All passive mobs have a first kill advancement
Works for 1.21-1.21.10, below 1.21.6 the background is not shown

Version 1.0.3
06/01/2026
Added first kill achievements and scoreboards for 
passive:zombie_horse, camel_husk, 
neutral:nautilus, zombie_nautilus
hostile:parched

Version 1.1.0
08/01/2026
Added first kills achievements for bosses (Ender_Dragon and Wither)
Create "Absolute Zombie Slayer" advancement, gained by killing Zombies, Husks, Zombie Villagers, Zombified Piglins
Hidden "Ultimate Zombie Slayer" advancement
Both titles are added to "hostile" page, "Drowned" and "Zombfied Piglins" are switched to the "Hostile Page", to be next to the other zombie types, following the "Absolute Zombie Slayer" advancement
"Illager Collection" added 
Added the plural suffix to some titles that didn't have it
"Absolute Skeleton Slayer" and "Ultimate Skeleton Slayer" added, same as Zombies, they were all moved to share the same root
"Zombie Collection" and "Skeleton Collection" added, "Absolute" titles were moved on the "Adventure" page
Added "zoglin" for "Absolute Zombie" title as well, because of hostility, removed "zomfied_piglin" from it
12/01/2026
Added "Piglin Collection", piglin was moved from the passive advancement tab to hostile, the location in the code is the same, the root was changed

Version 1.2.0 -> Version 2.0.0
20/Feb/2026
Added day_counter
Made "Absolute" and "Ultimate" hidden
Added "Arthropod Collection"
Create "Golem Collection", in neutral page, and added copper_golem.kills, as it seems it was missing
Change the image from "Piglin Collection" from piglin_head to golden_sword
Created "Village Collection" in passive page
Two more achievements for villager.kills

Creating a rarity system for all the mobs, which will determine the kills needed for the "Slayer" title for each one (helped by Gemini, because I do not know as many things about each mob, I'm open to feedback):
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Common: 1000
Passive: Chicken; Cow; Pig; Sheep; -> Butcher
Neutral: Cave Spider; Spider; Drowned; Enderman; Zombified Piglin; 
Hostile: ~Creeper; Husk; ~Magma Cube; Parched; Silverfish; Skeleton; ~Slime; Stray; Zombie; -> Self-defense

Uncommon: 500
Passive: Cat; Cod; Donkey; Horse; Salmon; 
Neutral: Bee; Endermite; Fox; Goat; Llama; Nautilus; Piglin; Polar Bear; Pufferfish; Wolf; Squid; Strider; 
Hostile: ~Blaze; ~Bogged; ~Ghast; ~Guardian; Hoglin; Pillager; Vex; Vindicator; Witch;

Rare: 100
Passive: Bat; Camel; Copper Golem; Frog; Glow Squid; Mule; Ocelot; Parrot; Rabbit; Snow Golem; Tadpole; Tropical Fish; Turle; Wandering Trader; | Camel Husk; Skeleton Horse; Zombie Horse;
Neutral: Dolphin; Panda; Iron Golem; Zombie Nautilus; Trader Llama;
Hostile: ~Breeze; ~Creaking; Phantom; Shulker; Wither Skeleton; Zoglin; Zombie Villager;

Epic: 25
Passive: Allay; Armadillo; Axolotl; Happy Ghast; Mooshroom; Sniffer; Villager
Neutral: 
Hostile: Evoker; Ravager; Piglin Brutes;

Legendary: 5
Passive: 
Neutral:
Hostile: Elder Guardian; Ender Dragon; Wither; Warden;
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Villager title changes, completed, 3 main titles, 2 hidden ones
Solved errors, mistakes, in some collections, and for "mule" title

Next, don't forget to rework the "Absolute" and "Ultimate" titles, based on the new max kills

21/Feb/2026
Removed "root" for bosses, now they are in "legendary_collection"
"Cubic Collection"
"Fly Away Collection"
"Bastard Collection"
All collections now have the "goal" frame
Next stage: create for passives and neutral (same page); create slayer advancement for all (or alternatives)
passive-neutral ones are the ones with "_" in front
"Farm Collection"
"The Persistent Ones"
Zombified Piglin to Zombie Collection
Removed the persistent ones and thw wither from zombie and skeleton collections
"I am under the water!"
renamed salmon_kill, as it was named ocelot_kill
"The Pride of the Waters!"
"Brother Bear!"
Renamed "golem_collection" to "_golem_collection"
"Ride it!"
"These Guys!"
"A Friend!"
"And then there were three!"
Advancement for all of the new collections, neutral page will be left for intermediary advancements
For the intermediary, some that would group more together or others that would just be doubled or slightly different

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Undead -> Zombies and Skeletons Collections 
Armies of the Dimensions -> Illiger and Piglin Collections