So far, all three Shadow Riders that Jaden had defeated contained a special shadow charm that was either lost or dropped:
-Nightshroud's mask was absorbed into a card.
-Camula's Necklace was dropped as her sould was being taken by the Illusion Gate. She is the only one so far to make a reference to the shadow charm when she talks to Jaden about her past ( Field of Screams, Part 3).
-Taniya's Glove or Gauntlet is left behind when she flees in her tiger form.
Also note that the glove/gauntlet and Camula's necklace both have the Eye mark that the Milennium items had in the original Yu-Gi-Oh series.