Animus said after Natsu transformed: "you're also a dragon!?" then after Natsu was beating his ass up a bit he then said "I have recognized you, your true form. You're the one who destroys everything. END." How can you explain that he recognized his true form after he claimed he was a dragon? Why would he even say that if he was a dragon in the first place?
What is "Dragon Force power"? Is that even canon? Natsu's Dragon Force was on both sides of his face, it just looked like it was on one side.
That makes no sense. Why would he half-transform into a dragon when the antibodies prevent him from turning into a dragon
at all? Zeref even said "I wish you had the power to turn into a dragon END". Meaning he can't transform into a dragon. If you claim this thought then why didn't the other 4 dragon slayers half-transform too? There's never been any half-transformation in-series.
Where did you get it was black flames? It's never been in color what kind of flames it is so we can't say it was black until we see it. The only canon coloring we got was on the Vol 59 cover and those flames surrounding him are red. This pic kinda adds up that OharaLibrian made:
Plus Hiro has switched shit around before so that's not uncommon.
He wasn't aggressive when he killed Animus? Plus he retained his sanity when he fought Gray and listened to Erza when she stopped him. His Etherious instinct just came into play, all it was. Fam trust me, I was skeptical as hell like you and it's plot holes regarding the canonical timeline but it was END, it would of made no sense if he dragonized with antibodies in him.