Bill Cipher 2004
The primary antagonist and the most powerful character in the Gravity Falls multiverse, Bill Cipher, will make his appearance in your world of Minecraft through the mod titled Bill Cipher 2004! This mod will transform the Disc 13 world into Stranglegeddon.
Bill is a new character and does not replace any existing mob. You can encounter him in forest biomes. However, since he is quite a rare entity in our world, it may be easier to summon him using a spawn egg or by entering the command doing /summon demon:bill.
Bill’s model from various angles:
Front:
Side:
Back: 
Bill in Minecraft, just like in the cartoon, is a hostile entity. He will attack everyone except for monsters. 
Bill is attacking with Shalker bullets. His life total stands at 666 points. If you manage to defeat him, you will earn a Nether Star and some gold.
Installing Bill Cipher 2004 (.mcpack)
- Download the mod labeled as “.mcpack” below.
- Run the downloaded file to import the add-on/texture into Minecraft.
- Open Minecraft Pocket Edition and navigate to the world settings.
- Set the imported options for the world:
— Resource Packs.
— Add-on Packs. - Select the imported resource packs/add-ons in each section.
- It is recommended to restart the game client Minecraft PE afterward.
- Launch Minecraft Pocket Edition, enter the previously configured world Minecraft, and enjoy the add-on!