The woman calling herself Seraph is perhaps one of the most enigmatic villainess/heroine that the Defenders have ever battled. She is either a type of mystical/ mutant woman who has been an operative of several undercover agencies in the past, most being her homeland of Russia.
This tall albino woman with a long silver mane boasts the power of a fallen angel. Super strong and durable with strange extrasensory abilities and glowing eyes able to take down humans and machines alike with a sense of holy rapture.
She worked on her first assignment against The Defenders when she showed up at the Vision and Scarlet Witch's New Jersey home to capture the synthezoid. Seraph was teamed up with Harridan, a wicked hag with the power to drain the life energies from others, and masqueraded as Cloud's older sister, an apparently teenage girl with the ability to transform into a gas state. Seraph than battled the Beast, Scarlet Witch, Ice-Man, and the Vision and almost succeeded until the Gargoyle defeated all three.
After another round of attacks against the Defenders on behalf of the Secret Empire, Seraph revealed her true connections. Showing that she was an undercover agent of the K.G.B and not truly Cloud's sister. She also helped defeat the Secret Empire and the Mutant Force alongside the Defenders.
Seraph however has not resurfaced in years and her current connections and location is a mystery.
It appears that Seraph possesses certain special mental abilities and meta-human physical powers. It is unclear if they are mutant or mystical in nature as she has given little insight to her origins.
Seraph has demonstrated empathic capacities, the ability to visually and verbally hypnotize organic and robotic individuals. Her "Celestial Choir", which combines both abilities in unison, sends individuals into a deeply serene state of "Rapture".
She also has displayed intense stamina and seems impervious to minor degrees of injury. Her reflexes and her reaction time also seem to be exceptional.
Seraph also has shown superhuman strength, the extent is not known. She was able to stand down the Vision in hand to hand combat and knock him unconscious and sling his form over her shoulders casually. Given that the Vision weighs up to 600 pounds this suggests that her strength level is not neglible, although definitely not in the same class as She-Hulk or Valkyrie. She can handle heavy weights of approximately 600 pounds & more without any visible discomfort or strain.
Seraph has had training in unarmed combat to some level of degree, she has exhibited hand-to-hand capacities in several of her missions against different groups. She is an expert mistress of disguise and has had intense training in investigation, languages, and intelligence gathering as a spy by the K.G.B.