Do you feel that in your Minecraft worlds there is little difficulty? What enemies are not sufficient for you? Check out this mod.
Invasion Mod 1.7.2 and 1.7.10 is a mod that allows us to live the battles in Minecraft with a lot more action and difficulty. This is possible due to changes in the behavior of the mobs in Minecraft, which makes them more dangerous than ever, while increasing the amount of enemies that will come to kill you.

Detail and Download here : Invasion Mod 1.7.2 and 1.7.10

Homepage: Mods for Minecraft