I know what is best for you
I have always known these things
That's why I've pulled your strings, tonight
You must learn to listen to me

The Book of Truth and Joy
- Anon.

The Shadow doesn't just have to rely on tricks, trade and being a nag in the backseat. It can, with luck - or proper timing - take over the body it shares with the Wraith. This state of being, known as Catharsis, isn't easy for a Shadow to pull off. That doesn't stop them from trying, though. 
In order to enter Catharsis, the Shadow must spend a three dots of Tainted Essence, and roll its Angst against the Wraith's Resolve + Composure + Eidolon. Success means that the Wraith slips into a coma of sorts while the Shadow takes over the body for a Scene per success scored over the Wraith's successes. Failure means nothing happened at all.

While in charge of the body, the Shadow can do anything the Wraith can do. It moves the body, speaks with the Wraith's voice and appears perfectly normal. It can spend the Wraith's Willpower and Essence, and gain them both back, and it can use her Numina and Advantages as well. It cannot, however, use its Thorns, spend Tainted Essence to fuel Numina or heal, or attempt Dissolution {or a Harrowing, for that matter}.


Taking Over Easier:
Under normal circumstances, the Shadow doesn't have a very good chance of succeeding against the Wraith. These chances are lessened even more by the Wraith's  possessing the Eidolon Background.

However, there are some circumstances when the roll is much easier, and Wraiths need to be very careful of them:
* Shadowstate: When in Shadowstate, the Shadow can make the roll as though its Angst were three higher than it is. It may only try this once per Shadowstate.
* Death Triggers: All Death Types have a specific "Trigger" that cuts through the Wraith, right to the core of her being, and gives the Shadow a slightly better chance to take over. In these cases the Shadow can make the roll as though its Angst were two higher than it is. It may only try with this increased chance once per day, even if the Wraith encounters Trigger after Trigger.
* Various Modifiers: The Storyteller may decide that something the Wraith does makes her especially susceptible to Catharsis, just then. This might be anything from giving into the Shadow's ideas a little too readily, or going dangerously close to the Shadow's Type in thought, word or deed. Such Modifiers should ideally range between +1 and +3, depending on the severity of the Wraith's indiscretion.

Cost: 3 Tainted Essence
Dice Pool:  Angst vs. Resolve + Composure + Eidolon
Action:  Contested
Dramatic Failure: N/A

Failure: Nothing happens, and the Shadow has spent Tainted Essence for nothing.

Success: The Shadow takes control of the body, as described above, for one Scene per success
Exceptional Success:
The Shadow takes control of the body for an entire day and night {24 hour period}