Duplication glitches are a way to dupe items. This allows players to have endless resources.
hyperdefined has stated that he allows dupes for a short period of time on purpose for players to collected needed materials.
Donkey Dupe 1
The donkey dupe was the first dupe that was used on the server. It was made aware of by Conga0. To do this method, you needed Future Client.
- Put a donkey on a chunk corner. Put the items in it's chest.
- Type ".entitydesync dismount," then type ".hclip 255."
- Wait a few seconds, then type ".entitydesync remount."
- There will be two donkeys. Take the items out of the one you are on, then hop onto the other one and collect the items again. You duped the items.
This was "patched" by hyperdefined when he disabled donkey and llama riding from the server. You would get a message saying "This action is currently disabled" when right clicking on a donkey or llama. hyperdefined then later reported the issue to PaperMC, and they fixed this dupe by backporting a feature from 1.13+. This patch from PaperMC fixed this dupe on all servers.