The Dark Side of the Moon
From left to right:
Descent, Eclipse (the only name I made, as the second stallion didn't get a name) and Nightingale.
And here, some headcanon:
The Shadowbolts originally weren't real living ponies, just simple entities created from magic by Nightmare Moon, to corrupt the Element of Loyalty. But when Luna was set free by the Elements of Harmony, the Shadowbolts were cut of and came to real life. Since then they live in the Everfree Forest and planing how to take revange for their mistress' "murder". Also, it's a small thing, but as originally they weren't real things, they don't have cutie marks.
Characters and MLP:FiM (c) Lauren Faust, Hasbro
Artwork (c) me
No stealing. Thank you.
I have one aswell: In mine, Nightingale does exist, she's Spitfire long lost sister. Long lost because she used to be a Wonderbolt. except she took her pride way too far by using her sister's sense of family caring to do dangerous tricks. Unfortunately for her, Spitfire reported her to the superior of the time, causing Spitfire to witness Nightingale's banishment from the Wonderbolts.
Full of hatred toward her sister, she sweared vengeance toward her and so she left to found the Shadowbolts, a group of ponies who has something against the Wonderbolts and the Pegasi society in general.