If you were about to loot a chest and then delete MCA files after closing Minecraft, all looted items will appear back in their chests, which allows item duplication glitch, and also duplicates every entity spawned by the game.

1. Find a nearby chest

2. Close Minecraft

3. Open "Run" program with "%appdata%"

4. Go to .minecraft\saves{world name}\region

5. Delete all MCA files here

6. Reopen world

7. All entities and chest loot have been respawned, allowing item duplication glitch.

This only works with naturally-generated chests and entities!

You will also lose all of your builds, so make sure to do this after you created the world!