Check what the Necklace can do.

What does The Necklace provide to the user?

Possession:

The user has the ability to take over the person he wants to be. In order to possess someone, The user can either phase through them or by passing the entrance of the User's insides.

Upsides:

You're invisible to any danger the world has to offer.

No one can see you.

You have the ability of a ghost.

There's no time limit. Feel free to use this opportunity to explore the world or stalk somebody.

Downsides:

No one would be taking control of your body, while you're in your ghost form.

You can only possess one person at a time. You can only switch bodies, if no one's occupying it.

Soul Trapping:

The user has the ability to separate the Victim from their own body trapping the victim's soul to the Necklace.

Upsides:

The trapped Victim would be unconscious not knowing what happened during their sleep.

After going back to your original body, You have a choice to release the victim's soul or not from The Necklace.

You have a limit of 2 souls to trap.

Memory Browsing:

While in possession of the victim's Body, The User has the ability to browse the memories the Victim.

Upsides:

You'll have no problem fitting in.

Downsides:

The more memories you browse, You'll be convinced, That You're the actual person.