So there is a bit of background to this drawing here and why Axis looks the way he does compared to your average Flygon.

A long time ago, Axis was exposed to radiating energy produced in some misty-like woods while tackling exploration myths within Sol's world. It was there he encountered Giratina by chance and the demon mon's presence affected that radiant energy drastically causing the flygon to become weakened.

Upon the Giratina finding Axis, Axis beseeched the Giratina for their help, though the Giratina didn't plan to help the Flygon at all. The Giratina did something that caused Axis to lose consciousness and wake up as a half Giratina, half Flygon hybrid. A cure was immediately worked for but to no avail. Axis was reaching the end of his rope when he suddenly changed to his old self again (coincidentally on the midnight of the first of November). He'd thought he'd gotten rid of the curse only to find when October rolled again he'd enter that state again.

In this current day and age, Axis has come to terms with it and after Mabel finding out, she'd thought it to be a cute addition to his Pokesona.

Mabel the Gardevior belongs to Lunar-Kuto
Axis Milo belongs to me.
Art done by an earlier me.