This is how Ryan vs. Desghidorah goes in Rebirth of Ryan.
and finds Desghidorah in the sky firing at Canterlot
Ryan F-Freeman: Are you ready for this?
[Desghidorah roars, accepting the challenge]
[Desghidorah fires his lava gout energy bolts from all three of his heads at Ryan but he dodges]
[Desghidorah flies after Ryan and does everything he can to defeat Ryan]