مToneri is "The Last" of his clan. He was born without eyes and was raised in solitude and darkness.

Toneri steals Hanabi's eyes and awakens the Tenseigan. He is able to enter the Tenseigan Chakra Mode (it's kind of like how one can enter Susanoo when they awaken the Mangekyo or Rinnegan).

Tenseigan (Reincarnation eye) is apparently the final form of the Byakugan. It's powers rivals that of Rikudou's maybe stronger.

Source: The Naruto Official Movie Guidebook (Written by Masashi Kishimoto). More info to come soon.