Mental invisibility is Afton's power to make himself psychically invisible to others.
Afton's power allows him to be unseen by others. This power is mainly an illusion that works by making pursuers think he is invisible or unable to see him when they look his way.
It can also be used to hide someone if Afton is directly standing in front of them, but this talent isn't as reliable as a power that provides protection for other people.
It has been explained that this power is very limited and much weaker than a real shield in that it can only "shield" the user. And if someone has a strong ability of focus, they can easily see past the invisibility. Since this power takes place in the mind, it most likely has no effect against Bella's shield.
Afton's gift provided him a position within the lowest ranked guards of the Volturi. However, his position was kept permanent due to his more powerfully gifted mate, Chelsea, who maintains the coven's organization with her power to control emotional bonds between people, which makes her a key member to the coven's functionings.