The Mystery Egg (also known as ?-Egg) on them and somehow the dot can turn into a creepy grin. These eggs are formed by Lulu using the power of ruby necklace that she gives to a person that seems "lost" and unsure about their desires in life. She activates its power by saying, "Just do what y'all wanna do!" (Yataro kotobai yapare ekage!). The person's Heart's Egg's becomes corrupted and forcibly leaves their body, born from the desire of a particular wish.
They exhibit the same powers as a regular guardian character, such as character change and character transformation, which in most cases occur when the person is provoked. One will have a ? bearing on their head and will cause chaos. Because they are still human, Amu can encourage them with words and once the person realises their mistakes the ? bearing will then change into an X and a silhouette of an X-Egg will appear above their form. During this dormant state, Amu can then purify the person and the egg together.