Requires the library mod Collective.

This mod is part of Serilum's Customization Bundle mod.
Configurable Extra Mob Drops is a server-side mod which adds the ability to add extra items to drop on death for any entity. On first load, it generates a config file. You can add items manually, or use the commands in-game. Any items with NBT tags such as enchantments and written books are supported. Modded entities are also supported, just make sure to remove or rename the config file in between adding mods which add custom mobs. If the file does not exist, it'll be generated with all possible entity types.

The config file generated is located in './config/configurableextramobdrops/' named 'mobdropconfig.txt'. The drop chances are set via the command or can be changed in the config file as well.

Commands:
/cemd usage - Shows the usage of commands.
/cemd list - Lists all entity names which can be used in addhand and cleardrops.
/cemd reload - Reloads all manual changes to the mobdropconfig file.
/cemd addhand <entity-name> - Adds the item held in the main hand as a drop for the entity named <entity-name> with a 100% dropchance.
/cemd addhand <entity-name> <drop-chance> - Adds the item held in the main hand as a drop for the entity named <entity-name> with a dropchance in between 0 and 1.0.
/cemd cleardrops <entity-name> - Clears all extra drops for the entity named <entity-name>.

All commands require cheat-access.

Images:
The /cemd usage command:

The /cemd list command. Shows all entity names which can be used in /cemd addhand and /cemd cleardrops.

The /cemd addhand <entity-name> command. Adding a Spawn Pig egg item to the drops of a pig with a 100% chance:

The /cemd addhand <entity-name> <drop-chance> command. Adding a Spawn Pig egg item to the drops of a pig with a 50% chance:

The /cemd cleardrops <entity-name> command. Clears the egg previously set.

The /cemd reload command. Updated the drops after a manual change in the mobdropconfig file.

Example:
An example of adding a milk bucket to the drops of a cow on death. Using the /cemd addhand command:

Testing it out on a cow:

Woop! A milk bucket!

The config file:
Located in './config/configurableextramobdrops/mobdropconfig.txt'.

Vanilla entities:

And with modded entities from for example Animalium:

A config example where a zombie villager drops a written book with a 50% drop chance:

The result:

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You may freely use this mod in any modpack, as long as the download remains hosted within the CurseForge ecosystem.

Serilum.com contains an overview and more information on all mods available.

Comments are disabled as I'm unable to keep track of all the separate pages on each mod.
For issues, ideas, suggestions or anything else there is the Github repo. Thanks!