Ido

The Ido (Id) is a beast that lived within Yakumo Kurama's mind. The Ido was used to battle Naruto while Yakumo was painting which was removing Kurenai from existence.

Trivia: The id is a real thing. It is one of the three human psyches. The id is said to be the most dangerous because it is your deepest, darkest fear. In rare cases, people have truly believed that their ids have killed them in their dreams, so they actually die soon after in real life.