Well, lost the character page for him so here's a sketch that never made it.
Thunderbolt (from what I remember) came from the sun and was the reincarnation of a weather god. He was named Thunderbolt for his thunderbolt shaped mane, courtesy of Rainbow Dash after falling from the sun and crashing onto Apple Jack's barn, effectively loosing his memory.
Like Butterscotch he could use magic without a horn, but instead it came from his tail only. He could only use weather related magic, such as summoning a thunder cloud or storm. Overtime these powers developed and matured to include other weather related powers, his amnesia also lifting.
I had a good story planned out for him, but somehow I just didn't finish XD