The Chaos Heart is a powerful source of chaos that holds much darker power than the Dark Star. PaperMarioFan1000 used to have possession of it. In season 2, Dimentio controls the Chaos Heart.
The Chaos Heart is a dark source of power that when you summon it, The Void appears in the sky, which is an interdimensional black-hole like object that will destroy all worlds. The Chaos Heart is perfect for making a new world. The person who controls the Chaos Heart will be invincible.
But the Chaos Heart is not all that powerful, The Pure Hearts can counter the invincibility shield and it would be gone forever.
But if someone takes control of the Chaos Heart after the person before controlled they will also be gained invincibility.
"After studies, I've indicated that this dark artifact holds a lot of power! And looking back at my book, it says that the Chaos Heart was once used when some princess and a angry reptile king, this was used by a white man clad with a white gown and his lovely assistant, which was a female. Then he wanted to destroy all worlds and "create new ones." Because of a lost love. Very emotional."