The Millennium Puzzle is one of seven ancient Egyptian artifacts that have great power and stuff. It is currently owned by Yugi Muto. Although the Puzzle is said to have many super special awesome powers, the only one that has been revealed thus far is the Mind Crush ability, which involves firing some invisible energy from your hand and causes the target's mind to completely crash (hence the name). It was originally rumored that the Puzzle also caused Yugi to instantly reach puberty. In reality, the "Older Yugi" is an entirely different being; the spirit, currently known as Yami, is a powerful pharaoh from 5000 years prior Yugi's possession of the Millennium Puzzle (and was also, coincidentally, the previous owner of the Puzzle).