Emperor Grogar did not like the idea of Lord Tirek having a young Pegasus as his protégé. So he decided to use his dark magic to transform Cozy Glow into a half-Dragon, half-demonic pony. This form is similar to Grogar’s Titan form at the climax of The Return Of Tambelon. I had this head canon that Tirek and Cozy first met because Tirek was still in Tartarus when he used some of his remaining magic to communicate with Cozy Glow telepathically before they became pen pals in crime.

Cozy Glow @ MLP:FiM/Hasbro/Lauren Faust
Fan Art @ MelSpyRose