Yes! Wither storm! Your dream comes true! I bring you this addon come in and see it! It has 6 stages you can kill it if you are strong and clever enough.
The first stage:
It is still a withe .Just with a command block.It is going to kill everything but you can kill it easily.It can shoot wither head and attract blocks.
Health：999999
Strength：1313

The second stage——The fourth stage:
If you don't stop the wither storm in time,it will be packed by some unknown black object slowly.At the fourth stage it will totally grow 3 heads just like wither storm.
Health：999999
Strength：1313

The fifth stage——your final chance:
If you want to beat this monster the fifth stage will be your final chance. Now thousands of blocks evolve this monster.The laser from its eyes will kill everything.
Health：999999 999999

Disclaimer: This is an unofficial app for Minecraft Pocket Edition. This app is not affiliated in any way with Mojang AB. The name, brand and assets are the property of Mojang AB or its respectful owner.