With many recent revelations in Fairy Tail and introduction of new characters, the inevitable question plagues us all - Who is the Strongest ?
The options are :
Zeref : Labelled as the most evil and powerful mage in history, Zeref has mastered the black arts and is immortal.Can anyone be stronger than an immortal?
August : Part of the Spriggan 12, this old man was described by Makarov to be on another level from Zeref. With not much known about his powers everything at this point is speculation.But I doubt that he is stronger than Zeref.
Acnologia : Acnologia was one of the first dragon slayers and a part of the Dragon Civil War. Also, known as the Black Dragon, Acnologia turned into a dragon due to overuse of dragon slayer magic. He can assume the body of a human or a dragon. His powers are so great that he even killed Igneel. According to Zeref, Acnologia can rule the world if he wants to.
Ankhseram : With powers strong enough to curse Zeref and Mavis, Ankhseram is the god (or goddess) of life and death about whom we don't know yet. But I bet that a god (or goddess) would be pretty damn strong.
Mavis : Mavis was Fairy Tail's first master and one of its founding members. She was Zeref's girlfriend (sort of....well....it's complicated) and was cursed by Ankhseram. She appears to be a young teenage girl but is actually over a hundred years old. Even though she is only an apparition now, her actual body is sealed in a lacrima and is Fairy Tail's greatest weapon. What if Mavis is able to use her body? That'll be something.
E.N.D : The strongest demon from the Books of Zeref and the Master of Tartaros, E.N.D has not been awakened yet and his powers are unknown. However, Zeref himself believes that E.N.D is powerful enough to kill him. Someone who can kill an immortal will definitively be insanely strong. To add to this hype, E.N.D is known to be none other than Natsu himself. Natsu will be able beat all of the characters in this list one day but he may not be able to do so without his friends and 'nakama' stuff. However, if he awakens as E.N.D he will probably beat them all simultaneously. (Spoiler: E.N.D is not really the master of Tartaros, Its Mard Geer himself.)