10/10/17 - the update today has fixed the chicken doll and this is now working properly.
Short and to the point -
There are 5 voodoo doll types.
* Batiri voodoo doll (did this on a Batiri Darter)
* Dinosaur voodoo doll (did this on a Trained Compy that was with a Batiri Beastmaster)
* Yuan-Ti voodoo doll (did this on a Yuan Ti Swordsman)
* Undead voodoo doll (did this on Skeletal Archers near Camp Vengeance)
* Chicken voodoo doll (this works on any of the monsters listed above)
These dolls can be found in the Chult Treasures that you get when you dig up the buried chests using the new Chult maps.
Map locations thanks to NWO Uncensored can be found here -https://blog.nwo-uncensored.com/soshenstar-river-treasure-ma...
Each doll is associated with a mob type that you need to use the doll on. You have to use the batiri doll on a Batiri, etc. One thing to note is that these need to be used on the minion mobs like a Compy, Batiri goblin, etc. Basically the trash mobs that accompany the normal mobs.
You can only get 6 maps per week from the Patrol Quests and may not get the doll you need from a Chult Treasure box, so there is a little luck needed to get the doll you need.
Edit 10/19/17 - According to Ham Salad this may be glitchy while attempting in a group and may not unlock unless you perform all of the dolls solo.