World gen: World generation is entirely overhauled. Explore 80+ new biomes (Biomes O' Plenty) Improved villages (Recurrent complex and others) vast underground cave systems (YUNG's Better Caves and others) and even some awesome randomly generated dungeons (Roguelike dungeons and others)
Mobs: Mobs are significantly buffed in this pack. They can break and place blocks and behave more like a player than an A.I (Epic Siege) They spawn with armor and gear (Rough Mobs) and they get much more difficult the more you explore and progress. (Scaling health) Completely new mobs are added by the pack such as Dragons, Gorgons, Knights, Griffins, Ghosts, and many, many more that can be found. (Ice and Fire and others)
Dimensions:
OVERALL: Dimensions are stacked on top of each other. Bedrock in the two dimensions you can mine below (The overworld and the beneath) have the bedrock at y=0 replaced with obsidian. This isn't the only way into these dimensions, but its a unique twist you might not expect.
Nether: The nether can be mined into from the beneath. New biomes like the ones from the nether update are added, but with their own unique flair that's unique to this pack.
End: New biomes, new structures, new mobs, and tons of new progression.
Aether: A heaven dimension with 3 new structures. A "hostile paradise"
Atum: An endless desert with new structures and progression.
Twilight Forest: An endless mythical wood with new progression and armor. Some of the best gear in the game can be found here.
The Beneath: Expansive and immense cave systems that are filled with tougher mobs and valuable ores.
Betweenlands: The endless swamp. A mysterious land veiled in fog.
IT NEEDS TO BE INSTALLED MANUALLY, THIS CAN BE DONE BY DRAGGING AND DROPPING THE OPTIFINE FILE INTO THE FOLDER TITLED "MODS" IN THE PACK FOLDER. NOT ALL SHADERS ARE GARUNTEED TO WORK AND YOU WILL LIKELY NEED A BEEFY COMPUTER TO RUN THEM.