I have an idea for an item that contains a shadow. When it is opened the shadow leaps out and consumes the nearest shadow(usually the person who opened the bottle) By consuming the shadow it replaces the person shadow. I need some help coming up what it should do.

I want it to decently powerful, but also have a negative as it was sealed for a reason.

A few ideas I have so far.

1. It lets the user shadow step 1/day as a reaction up to 30ft.

2. It gives the user 1failed death saving throw at all times as they are a little closer to the veil.

3. It acts as a limited familiar. It can move up to 100ft from the user and act as a familiar, possibly even having 1/day ability to manifest the familiar into a physical creature for X minutes, and while your shadow is missing you have disadvantage on something(not sure what yet) and if your shadow dies while apart from you, it reforms during the next dawn.

4. It tries to corrupt the owner, I need help trying to figure out its goals, how it gets the user to do those goals and what it can offer as enticement.

5. If the user ever dies, it immediately takes control of the users body and attempts to flee with its new body.

6. Not sure how the user could capture the new shadow/get their old one back.