Monsters Level Up is a mod that makes all mobs level up alongside the Player as they progress through the game. Main story advancements will make mobs harder to kill.
The triggers are : getting Iron Armor, getting Diamond Armor, enchanting, entering the Nether and killing the Ender Dragon.
Requires Geckolib!
Mobs will gain new gear, abilities and behaviors. Some of them include :
Mobs spawning with potion effects and more gear.
Mobs being able to use shields and flint and steel/fire charges.
Undead mobs calling for reinforcements upon getting hit.
Creepers riding spiders.
Creepers disabling shields.
Skeletons switching between melee and ranged.
Drowneds riding zombie dolphins.
Spiders setting targets in cobwebs.
Mini-bosses can spawn in the world:
Skeleton Commanders ride Spider Mothers and buff nearby mobs.
Zombie Juggernauts can reduce armor points on hit and dash.
Wither Skeleton Horsemen ride Wither Skeleton Horses and are composed of one leader and two soldiers.
Killing those mini-bosses will reward you will materials to craft gear with special abilities.
New entities:
Spider Mother

Spider Mothers are tankier than normal spiders and deal more damage. On death, cave spiders will emerge from the corpse of the Spider Mother.
Lightning Rod Creeper

Lightning Rod Creepers spawn when it's raining. Once they get close to their target, they turn into Charged Creepers.
Zombie Dolphin

Zombie Dolphins can rarely spawn in oceans. They attack any creature in the ocean and will bring Drowneds closer to the player.
Wither Skeleton Horse

Wither Skeleton Horses can rarely spawn in the Soul Sand Valley. They are hostile and will set targets on fire and wither them. They can sometimes spawn trapped.
Wither Skeleton Horses can be tamed with Phantom Membranes.
Complete mod rework
Notable additions & changes:
-Skeleton Commanders
-Gilded Commander Armor
-Gilded Commander Shield
-Commander's Cutlass
-Commander's Flag
-Gilded Ingot (Dropped by skeleton commanders)
-Zombie Juggernauts
-Juggernaut Armor
-Breaching Hammer
-Breached effect
-Heavy Shield
-Heavy Plating (Dropped by zombie juggernauts)
-Wither Skeleton Horse
-Wither Skeleton Trap Horse
-Wither Armor
-Greatsword Of Souls
-Fire Vulnerability effect
-Wither Bone (Dropped by Wither Skeleton Horsemen)
-Zombie Dolphin -Spider Mother
-Acid Venom effect
-Achievements that show the current world difficulty stage
-Armor requirements now work with tags (can be modified)
-Reworked how mobs get armor and gear
-Reworked all mob behaviours
-The configuration file is now more complete with more options to modify the mod
This is basically a new mod. Make world backups in case older worlds get corrupted.
The scaling triggers feel very organic 👌