Stokia was an especially adept Bene Gesserit sister who was trained to be a guilt-caster. Stokia would sneak up behind her victims, when ordered by the Sisterhood, and diable them with psychic waves of energy. Coupled with Stokia's bringing up the great disappointment that the Sisterhood felt in the intended victim, the victim would soon be rendered comatose; and en-wrapped in their own guilt.
Tessia Vernius
Stokia was first successful in 10,188 AG when the Sisterhood paid a visit to Tessia Vernius on her home planet of Ix. The Sisterhood was greatly displeased as Tessia had decided to stop bearing children, simply because her husband Rhombur Vernius was impotent. Stokia and her three assistants rendered Tessia in a comatose state, and transported her back to Wallach IX.
Jessica Atreides
Her second attempt was much later in 10,200 AG when the Lady and Duchess of Caladan, Jessica Atreides, visited Wallach IX, and was offered the Mother Superior position of the Sisterhood, if she would simply kill Paul the next time she saw him. When Jessica refused, Stokia and her assistants moved in to render Jessica incapacitated. Jessica, who had pre-taugtht by a newly awakened and resistant Tessia; was able to beat Stokia off.
Margot Fenring
Far later, in 10,207 AG, the Sisterhood dispatched Stokia and her entourage' to Salusa Secundus to gain retribution on Lady Margot Fenring for her and her husband's role in the failed assassination of the Emperor Paul Atreides, nine years earlier. Margot and Hasimir had not consulted, and even shut out the Bene Gesserit order when they unleashed young Marie Fenring onto Muad'Dib. As Stokia attacked Margot with bands of negative psychic energy, Margot began crumpling under the intense guilt pressure. Hasimir observed through a keyhole his wife's predicament, and stabbed Stokia deeply in the back, and killed her.