I see more of a Unicorn, mystical animal Wings of a bird, horn of a ryno.It might seem unusual, but I can see Rapidash getting a Fire/Flying Mega. It could be based on a Pegasus (a winged horse) or maybe even Sleipnir, Odin's 8-legged steed from Norse mythology! The good thing about it is that it would most likely be an easy job balancing it for competitive play when creating stat boosts; it would become 4x weak to Stealth Rock, so that would always compensate for base stats that would otherwise make the Pokemon broken.
As for me I'd say Elektross