Hardercraft by Technic [1.17-1.19]

Simple change to minecraft since it always bothered me... At the start of the game with wooden tools you fight normal zombies and skeletons. With iron armour and a diamond sword in the middle of the game you fight normal zombies and skeletons. At the end of the game with full netherite gear and an elytra you're still fighting the same zombies and skeletons that you were when you started the game. So this datapack changes that with an 8 level difficulty scale.

Level 1 is regular minecraft, and once you get a piece of diamond armour it changes to level 2
Level 2 is slightly harder - mobs move faster and zombies can break doors.
Level 3 give mobs weapons
Level 4 gives them armour
Level 5 reduces the maximum amount of protection armour can provide
Level 6 alerts mobs to your position at all times
Level 7 gives mobs better weapons and armour
Level 8 is a nightmare. Mobs have similar armour and weapons to the player at that stage.

All levels are progressed through based on achievements, and you can see which difficulty level you're on with the separate "Hardercraft" advancement sequence. Difficulty is global and not based on individual player achievements, and whenever a new level of difficulty is reached, a big warning tells everyone in game, along with a short explanation of the changes made.