The Millennium Pendant, as Titan called it, was a fake version of the Millennium Puzzle used by Titan as he pretended to steal people's souls.
Using the pendant and other trickery, Titan simulated Shadow Duels, causing his opponents to legitimately believe that what they experienced was real (in the dub, they were said to be sent to the Shadow Realm). He used it against Duelists in the streets and after winning a Duel he would punish them with a fake Mind Crush. He was later hired by Dr. Crowler to scare Jaden Yuki away from Duel Academy. Titan took Alexis Rhodes hostage to lure Jaden to the Abandoned Dorm to Duel him. Near the end of the Duel, Jaden, with the aide of Winged Kuriboh, realized that the pendant was a fake after Titan claimed there were seven Millennium Puzzles, as opposed to seven Millennium Items (in the dub, it was because he called it the Millennium Pendant, instead of the Millennium Puzzle). Jaden threw his "Elemental Hero Avian" card at the pendant, causing it to break.