This a collection of mods that combine to revamp the entire world by changing biome block generation, dungeon structures, and dangerous mobs.
There is even a new dimension to explore, courtesy of The Undergarden mod.

Mods:
Additional Structures - Generates new structures throughout the world.

Architechury API (Forge) - Dependency.

Artifacts - Adds powerful artifact items that can be found in chests and dropped from mimics.

Awesome Dungeon - New dungeon structures.

Balm - Dependency.

Better Than Bunnies - Makes Bunnies look rather dapper.

Brutal Bosses - Spawns dangerous bosses throughout the world made from vanilla mobs.

Champions - Adds a random chance for a mob to spawn more powerful.

Collective - Dependency.

Craft the Totem of Undying - Makes Totems of Undying craftable.

CreativeCore - Dependency.

Creeper Overhaul - Adds biome camouflaged creepers.

Curios API - Dependency.

Customized Dungeon Loot - Makes it so custom items can spawn within dungeon chests.

Death Compass - A compass that points to where you last died.

Dragon Drops Elytra - Gives an elytra to whoever got the final hit on the dragon.

Dusk - Makes night time harder :)

Enchantly A Magical Expansion- Adds new enchantments and potions.

Expand Ability - Dependency.

Feature NBT Deadlock Be Gone - Dependency.

FlashFyre's Enchantments - Adds even more enchantments.

GeckoLib - Dependency.

Hunter illager - Adds a cabin structure with a hunter illager spawns in.

Just Player Heads - Adds player heads that you can spawn with commands or players drop on death.

Kobolds - Adds Kobolds and structures they spawn in underground.

Library Ferret - Dependency.

Macaw's Bridges - Adds blocks to make bridges.

Magic Combat Wands - Magical wands

Mahou Tsukai - Magic, Mana, Spells, etc.

Meet Your Fight - 3 new bosses that can be summoned using craftable items.

PlayerRevive - Allows you to revive other players.

Puzzles Lib - Dependency.

Repurposed Structures - Redesigns some structures to better suit their biomes.

Revamped Phantoms - Makes Phantoms much more difficult.

Savage Ender Dragon - Makes the Ender Dragon Fight Harder

Stalwart Dungeons - Adds more dungeon structures.

Terralith - Revamps the entire overworld's biome block generation.

The Graveyard - Adds graveyards and spooky mobs.

The Undergarden - Adds a new dimension to explore.

Tiny Skeletons - If you hate baby zombies, you will hate tiny skeletons even more.

Upgraded Core - Dependency.

Upgraded Netherite - Adds upgraded versions of netherite tools, weapons, and armor.

Useless Sword - Adds 70+ new swords which are not useless.

Void Totem - Adds a totem that will save you if you fall into the void.

Waystones - Adds waystones to teleport throughout the world.

XP Tome - A book to store xp in.

YDM's Spellsword - Adds magical swords.

Dungeons, Swords, and Magic