The Mob Duplicator is a mod created for SmallAnt's Twitch stream and YouTube video included below. What it does is really simple! Whenever a player with the duplicator active takes damage, all mobs within the configured range duplicate, including all data associated with them.
Getting started with the Duplicator is also very simple! Just type in the command: /duplicator {target} start
The players included in the target will now duplicate any mobs in the configured range whenever they take damage. To stop this effect, use the same command, except replace start with stop.
The mod also includes a config to help tweak the more specific features of the mod.