He clearly has an ehterious form as shown in chapter 504 when his hands became long. Besides zeref also mentioned that larcade was his strongest substitute in creating natsu. If igneel or even zeref didn't sealed of his memory then why didn't he remember his time with zeref or didn't recognize him. Besides zeref also said that he was indirectly involved in the creation of tartaros that is mentioned in the chapter 466. Mard geer was attempting to reunite all the demons of zeref based on legend of END. Zeref was entirely hoping for END to kill him despite having strong spriggans like larcade and bradman/bloodman. On top of that igneel hped him to extreme by saying acnologia was afraid of him even knowing acnologia's full strength. There are others hyping him up to like atlas flame, invel and dimaria( dimaria was so afraid that she even said that his power is even greater than that of god chronos). Lets be honest this plot was left like that due to its dark nature in a light weight series. Can you there was no casaulty on FT this whole war.
Author wanted to make FT a light hearted series and this was the most dark plot in the whole series on top of wanting natsu to be cliche MC( kind, nakama spouting bla bla nonsense).
Honestly irene was more of a heroine than villain. She couldn't kill her daughter and did go after acnologia rather than going after FT. Let's be honest this kind of saved FT big time, there was no one who could have come closer to her. She should have played role in the final battle with acnologia along with zeref.
Etherious forms aren't relevant to whether Natsu has an alter ego or not. Does Mard Geer's or any other etherious form change their ego? Answer is simple, no. Whether Natsu could have an etherious form or not has no effect on his mind. We have seen it from countless etherious, they are still the same person. They didn't seal his memory, simple as that. Show me a page that proves or stop assuming things out of nowhere.
Zeref said the exact opposite. Some reading comprehension is needed. Mard Geer found the book and made tartaros on his own. Natsu had no actual ties.
Zeref also agrees Igneel could've easily killed END, but didn't kill him because he loved him. Natsu clearly remembers his time with Igneel when he teach him dragonslayer magic, which rules out the memory sealing bs. Igneel wouldn't personally love an etherious he never saw before.
His hype has nothing to do with his ego. Only reason Acnologia could've feared END because he could eat magic, it is normal for him to want to eliminate Zeref's ultimate creation who had the potential to use more than magic.
In the end, all the hype came to be true. END defeated both Zeref and Acnologia, albeit without using his potential etherious powers. There is no actual difference, which is also the reason Zeref calls him END or Natsu interchangeably, because he is.
Just to point it out
Some people 
