This (Forge) mod extends the height and depth vanilla limitations. Always wanted to build beyond the 256, 320, or 512 height marker? ... well now you can go 1024 blocks up. What about going deep below the bedrock barrier?, in creative mode you can go beyond the bedrock, and build an impressive dark world 511 blocks below without leaving the overworld. while in the void, you will be able to see the sun, but there in no ambient light (must place torches, etc).
This is a quick demo from top height to the new depths of your world. Look at the highlighted areas. Forge only
__SK_'s Shattered World Limits - V4-1.17.1.jar - Added Noodle caves and ores to generate from Y -511 up
1.19.2 Update
World height is 1024, but you can choose from -64, -128, -256, or -512 depth. Also for worlds with Y-128 depth, the deepslate will start at aprox. -64 ... For worlds with Y-256 depth, the deepslate will start at aprox. -128... For worlds with Y-512 depth, the deepslate will start at aprox. -256.
Have fun!
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Will not work on 1.16.x or below
As of today, V2 (and up) is not Optifine-friendly - UPDATE - This might be permanent - Issue for 1.17.x only. NOT AN ISSUE FOR 1.18 OR ABOVE.
Cause: Flickers when it exceeds 256 blocks in height. https://github.com/sp614x/optifine/issues/5768
Q : But, why does it flickers below Y 256 using this mod? Issue for 1.17.x only.
A: The altitude is not measured from Y 0 to Y 256, it starts from the bedrock floor up. In this mod's V2+ the bedrock floor is at Y -511, meaning - from Y -511 to Y -255 your screen will not flicker. Anything above that point (Y -256 to Y 1024) is not Optifine friendly.
Updated to 1.18 Forge
If using 1.18.1 and above, no more flickers while using Optifine.