Butchery Add Mobs lets an animal from another mod drop a proper Butchery carcass or corpse when defeated, the same way regular animals do. You set this up by editing the text files inside the data pack's zip.
Edit the Animal List
1. Close your world first. Editing pack files while the world is running can cause confusion about which version loaded.
2. Open your world's save folder and find the Butchery Add Mobs zip file.
3. Make a copy of the zip somewhere safe, so you can restore it if an edit goes wrong.
4. Open the zip and find the text file for the animal whose carcass you want the modded creature to drop. For example, use the chicken file for a chicken-like bird.
5. Type the modded animal's name into the list in that file. Copy the format of the entries already there.
6. Save the text file and make sure the change is written back into the zip. Some archive tools ask you to confirm updating the archive. Then close it.
Test It In Game
1. Load your world.
2. Find or spawn the modded animal and defeat it.
3. It should now drop the matching carcass or corpse, ready for the usual Butchery processing.
The dropped carcass uses the vanilla carcass texture and model, even if the modded animal looks different. A plain-looking carcass means the link worked.