Wormwood

Per tree of Wormwood (that means chips of tree are aggregated), there can be one soul cursed, inhabited by the ancient spirit of the wormwood. These spirits each have different, evil, things they do, but also do a fair job of keeping under the radar and do well at framing blame on others. Touching any part of the tree will curse the toucher unless the spirit already inhabits someone else. Nobody knows how wormwood works, but they do accept that it is "cursed" because misfortune typically follows its pieces.

Ishmael, one spirit, carves eyes and other pictorials into the skin of victims whenever he finds himself alone with someone else. Otherwise, he lets the host body control itself and just blacks out (or overwrites) their memory of his take-overs.

Cael, another spirit, waits in hiding until it finds an "awesome" way to suicide its host, and then takes over.