Canaima

An evil spirit that invades people and causes them to fall into a murderous rage. At the same time, people may or may not turn into animals. 

Murderers and people seeking revenge sometimes evoked this spirit with the help of drugs and magical rituals. The usual method of killing a target is stealth and a poisoned arrow. So it's like a berserk ninja werewolf. Further legends speak of a certain tree whose sap, if rubbed into the skin, drives you crazy and turns into an animal, usually a tiger or a snake. Throwing this juice at people seems to have the same effect. 

Some tribes believe that either a spirit or a person possessed by it can use an invisible poisoned arrow, in fact a kind of magic projectile, and this arrow leaves a blue spot somewhere in the target's body. 

Even if kanaime manages to kill his target, in three days he has to visit the corpse and lick some of its blood. This can be seen as an offering to the spirit of Kanaim to leave his body. If he cannot do this, he cannot return to his tribe, remaining a criminal that even his family must kill. He also plunges further into madness until his death, because the spirit is dissatisfied. 

There is a large-leaved plant caladium, which serves as a kind of magical detector of the approach of the spirits of Kanaim. When one of the latter approaches, the plant emits a long, low whistle and somehow shakes the target's hammock to wake her up.