Fairy Tail final season has Natsu and Zerif facing off. This follows the same line as the manga which means that we get to see Natsu fire dragon king mode. Natsu strongest mode it uses power of Igneel which is a dead power allowing him to hurt Zerif. The one thing is in this mode he cannot devour fire magic. But that sacrifice seems like nothing compared to the power he has. See how it looks animated below.
Article:https://comicbook.com/anime/2019/02/04/fairy-tail-natsu-zeref-fight-fire-dragon-king-mode-anime/
As always thank you for reading.
