This Soul Shards: The Old Ways mod will allow you if murder to collect the souls of mobs in the stones, and then you can summon them in greater numbers. You will also be able to craft new tools and weapons.
How to install Soul Shards: The Old Ways
- Download and install Minecraft Forge
- Download mod
- Do not unzip it, copy to C:\Users\User_Name\AppData\ Roaming\.minecraft\mods