Shield penetration is Renesmee Cullen's theorized ability to destroy or penetrate a mental shield. Aside from this gift, she also shows the power of tactile thought projection, which she can use to show people her thoughts and memories with this power to break through their mental defenses.
Renesmee can use this power through tactile thought projection to penetrate a shield and place her thoughts into their minds without their defenses hindering her. It is not yet known if her penetration works only on Bella's shield, or any other like that of Renata, a high-ranking member of the Volturi, and Aro's personal guard. It is, however, thought that she can communicate with anybody she touches without their mental defenses keeping her at bay. It is also unknown if her power operates by penetrating the shield, sidestepping it or neutralizing it completely.
Limitations
This power works via physical contact with a target. It is unknown whether she is able to break through physical shields like Renata's. However, its effect may more limited than her thought projection due to Bella being human when she passed it on to Renesmee.
Renesmee's gift of shield penetration is described as being the opposite of her mother's power, much like how her other gift of tactile thought projection is thought to be the opposite of her father's. There are indications that she can consciously control both her gifts.
Elements of this power have been thought to be inherited from Charlie Swan, who has a shielding ability mental similar to Bella's, though much less powerful than Bella's.
Breaking Dawn
"Maybe she took your talent and flipped it, too."
―Edward's theory of Renesmee's ability to penetrate Bella's shield.[src]
Renesmee proves to be the first being with a psychic power strong enough to pass through Bella's mental shield when she shows Bella her first memory she has of her.
