Slyther Shattermaw (who generally just goes by Sly) is an earth pony stallion that resides in Stalliongrad. He is the resident Regulator of the city and is featured in Fallout: Equestria - The Last Sentinel.
Little is known about Sly other than that he is a Regulator, a faction of vigilantes that is mainly concentrated in the Capital Wastes. They aim to being law and order back to what's left of Equestria- law through the gun. They have a unique if not slightly unsettling tradition of keeping hooves or talons or denote kills. It is presumed that Sly was with Frost when the people of Stalliongrad retook the city from raider control.
Sly is a giant of an earth pony stallion. He is described as having a deep-blue coat with odd red coloration around his hooves and muzzle, blue eyes, and a dark-brown mane and tail. He often wears a Regulator duster.
He has a very upbeat personality, cracking humor and generally being very friendly. He can be a bit clumsy at times, however.
Sly is a savant when it comes to explosive ordnance, able to skillfully and expertly deliver rockets and grenades as necessary to avoid collateral damage (usually) and maximize area of effect. He is also very proficient in close combat and a decent sharpshooter.
Sly possesses a battle saddle fitted with twin M220 FLASH rocket launchers and a set of powerhooves. Though not yet depicted, he also has a lever-action rifle that he calls "Clipper".