Legacy Bedrock Preservation (1.18.2 Forge)

Have you ever updated an old Alpha, Beta, or legacy world (pre-1.18) to the modern era, only to find that the bottom 5 Y-levels of your original chunks' bedrock was completely erased and replaced with deepslate? This mod is the solution!

🛡️ What It Does

Normally, Minecraft's BelowZeroRetrogen engine forcefully wipes out your historical bedrock floor between Y=0 and Y=4, overwriting your original blocks to make room for the new subterranean terrain.

This lightweight utility mod completely blocks that deletion script. It freezes your original chunk data perfectly at Y=0 through Y=4, keeping your old bedrock and custom basements completely intact. Meanwhile, it forces the 1.18 noise-cave algorithm to seamlessly weld the new deepslate underworld right flush beneath your feet starting at Y=-1, with zero air gaps.

⚠️ IMPORTANT: One-Time Conversion Workflow

Because this mod alters chunk data structures permanently during world migration, it is meant to be used as a one-time gateway tool. Do not keep it in your permanent everyday modpacks. Follow these steps:

1. Create a temporary profile in CurseForge for Minecraft 1.18.2 (Forge).
2. Drop this .jar file into that profile's mods folder.
3. Drop a copy of your legacy pre-1.18 world folder into that profile's saves folder.
4. Click Play and load into your world. Walk or fly around your main base chunks to allow the new negative deepslate data to generate.
5. Save and close the game. Your custom-preserved geology is now permanently baked directly into your world files!
6. Open your profile folder, open the saves directory, and Copy your upgraded world save.
7. You can now paste this fixed world directly into your regular, official vanilla Minecraft Launcher (%appdata%\.minecraft\saves) and safely update it to 1.21+ or any future version completely vanilla! The game will retain your custom bedrock ceiling forever.