Dogs will bark, cats will screech, squirrels will chatter and run, and even fish in an aquarium will try to hide. The spirit must suspend all brain activity in his host when he takes active control. During this time, he cannot access any of his host's thoughts or memories, and all actions taken by the host will be reflections of what the spirit in possession does. However, the host's mind can never be returned. As always, the GM has final say on what character designs are legal, and which are illegal.
Possession is the key to most actions within the spirit world.
The spirit can be hidden amongst the living, protected from the harsh spirit world beyond. For most spirits, it's also the only way to make a difference in the real world they see every day. The rules behind possession are simple, but the effects are far-reaching. The Merge difficulty increases one level for every extra attempt made on the same person within ten minutes. It also increases one level for every five failed attempts on the person per day.