User blog comment:KaiserLos24/New Shadow Isles Champion- Kalista (Maybe :P)/@comment-5921332-20141023235321/@comment-12049719-20141024014706

I doubt it's Senna is the one behind this because her soul was caught by Thresh (but her physical body leaves more questioning, though), but the whole treason and vengeance thing does seem plausible. We might possibly awaiting a human (or some other race) that was transfigured when he/she stumbled upon the Shadow Isles, seeking vengeance and punishing those who have done evil. Kind of like a dark hero, possibly?