After seeing the movie Annabelle: Creation I thought, why not have a mod for this? So here are the details:
A porcelain doll can be rarely found in Woodland Mansions (it reminded me of the house owned by the Mullen family in the movie). It can be placed, and seems harmless enough due to the holy papers found stuck to the walls around it (meant to keep the demonic spirit in check). However, once placed outside that area, the real horror begins. The player can occasionally see a little girl running around, this is Annabelle "Bee" Mullen. Or so it seems. If you get too close to her, the demon reveals itself and attacks.
Health: 25 hearts
Damage: 1.5 hearts on easy, 2.5 on Normal, 3.5 on Hard
Speed: 1.5x that of a spider
If the demon encounters a villager, it has a chance of turning it into a possessed villager and then disappears. This chance is the same as zombie villager conversion, except it has a minimum 10% chance on easy.
Possessed Villager (Looks like a villager, but with a slightly duller skin and has the same green eyes)
Health: 15 hearts
Damage: 1 heart on Easy, 2.5 on Normal, 3 on Hard
Speed: about that of a Vindicator
If the possessed villager dies, the demon spawns where they died and either attacks the player, or if villagers are nearby searches for the nearest one to try possessing.
You can craft a Raggedy Ann doll with 4 wool of any color and it can be possessed by the demon, or you can give it a demonic spirit by crafting the doll with 4 soul sand and 1 wither skeleton skull.
The Disciples of the Ram cult will have cultist camps randomly spawning around the world, with a rare chance for the original cloth Annabelle doll to be found in a chest. Cultists will attack you on sight, and drop their robes, hood, or shoes rarely.
To purify the doll and stop the demon from coming back, you simply need to place the doll in the center of a 5x5 quartz circle (the circle must have a gold block in the center), and pour holy water over it. Holy water is crafted with a bottle of water surrounded by 4 glowstone dust, or bought from a cleric villager for 10 emeralds. Holy paper can be looted from Woodland Mansions or crafted from a book and quill and 4 glowstone dust. It is meant to hold the demon back, but will not get rid of it.