Lulu's ruby necklace
The ruby necklace is an item handcrafted by the anime-original character Lulu to corrupt a Heart's Eggs into Mystery Eggs.
Ruby Necklace[]
Once it is worn by a person, their Wishing Egg will become a Mystery Egg. This egg has the same powers as a regular guardian character to influence the corrupted person, such as Character Change to wreak havoc around the city and then enact a corrupted version of Character Transformation.
The necklace has also shown capability to corrupt people who have Guardian Characters as well, examples being Yua Sakurai and her guardian character Cecil.
Lulu mainly uses the necklaces on a person who doubts their skills and their dreams, and she must be in Character Change with Nana during the transition.
When Lulu parts ways with Amu in Episode 89, Lulu gives Amu a powerless Ruby Necklace as a gift.