It's been almost two weeks and still no one has replied, does that mean Flygon is perfection and cannot be improved? I'd like to think so.
If i could, i'd change it to bug/dragon type, just to give it some uniqueness - can't really say if that would be a buff or a nerf. The big ice weakness would be reduced, but there's not much other benefit, and it would lose electric immunity.
buff, make it cancel will-o-wisp too
while it's obviously an amazing ability, the fire immunity is almost useless considering kyogre only takes 25% from those moves anyway
now its counterpart's ability, that could use a nerf