Since he was young, Dark Star has had to face many a challenge for his image.
Charcoal fur, black mane, and even the same red eyes as the once villain Sombra. Sure, there were tales that the evil King had reformed, but no one had seem him in a long time, leaving Dark Star at the mercy of both children and adults alike accusing him of being a future abomination.

The day he earned his Cutie Mark didn't make things any easier. Having the image of the Grim Pony on a tome for a mark seemed to be an ill omen for all.

But the day he earned it was what set his path in stone. It was the day his mother died, and the day he wondered...what happened to ponies when they died?

Luna heard the stories. She heard the rumors and the gossip plenty enough even in her court.
Tales of a pony resembling Sombra going about, visiting ponies on their death beds just before they left Equestria for good. The Harbinger, they called him.

She was going to learn the truth, and she knew exactly where she would find him. After all, poor Shining armor never ascended like his wife. His time was at an end, and Luna knew the Harbinger would not pass up such a large figure finding his path to the afterlife.

Bow Shock was their only chance.
The undead army was approaching, the surprise attack by the necromancer giving them no time. The Princesses were too far away to get there soon enough. Ponies would die.
He couldn't let that happen.
So Bow Shock took the one route he had. The one weapon at their disposal that could end this with only one death.

All he needed was a few moments in free fall, if he didn't get a boost, and even the famous Rainbow Dash would be jealous. Too bad he wouldn't be around to see her face after this.