User blog comment:FairyRaven/Fairy Tail Chapter 356: Tartarus arc - Prologue, Review and Commentary/@comment-7505640-20131020033003/@comment-1359322-20131020042029

Not really a bonus or anything since E.N.D. was already mentioned by Atlas Flame, Levy confirmed that it's a Demon that is incomparable by the types of Deliora and Lullaby. Cobra just confirmed that E.N.D. is leader of Tartaros.