Alexei

 is a young abnormal first encountered shortly before Dr. Will Zimmerman joined the Sanctuary Network. His abnormality is a snake-like extra limb that can easily kill people, but acts as a defensive mechanism when he is afraid. He is said to be a result of the radiation from the Chernobyl disaster.

Biography
Fearing he would be taken away and experimented on by the government, his parents, who loved him deeply, sent him away to America for his own protection. As Magnus explained, many children like Alexei are adopted by well-meaning immigrant families and many of them have certain problems either mental or physical. Alexei's problem however caused him to be shunned by his adopted family especially when their fear kept agitating the appendage. Also, the family who adopted him were religious, and this caused them to see Alexei like some kind of a demon or monster. They kept him hidden and locked up in a room in their apartment, only letting him out to eat.

Physiology
Tests on him revealed the extra limb is a massive genetic mutation incorporating bone, flesh and cartilage, but it does not appear to be parasitic and is actually symbiotic. It is also vaguely self-aware and can act on its own without Alexei's consent when he is scared; attacking any immediate threat with a radioactive tip. Alexei himself doesn't appear to be affected by the radiation. The limb is also very strong, as it could pull him across a ten-story building.

The limb is attached to Alexei by what look like a form of pouch in his side where it most likely receives nutrients when Alexei eats; though the tentacle does have a mouth and teeth it may be possible that it can eat on its own. When the tentacle is not stirred or defending Alexei it will rap it self around his chest.