Forst Mane is a Raider unicorn, encountered by Cogwheel on his first day outside the Fluttershy Medical Clinic, he woke up in.
Frost Mane was part of a much larger group of Raiders that had been using the Clinic that Cogwheel woke up in, as a base of operations. The majority of the group were slaughtered by an Alicorn who claimed to be an agent of Luna, all except Frost Mane who she told to run.
Frost Mane ran from the clinic and would try to rob Dust and Precious. He failed when Cogwheel arrived and fought him, Cogwheel eventually managing to knock the unicorn stallion out cold. Frost Mane awoke and tried to bluff Cogwheel and the group with an unloaded shotgun, but Cogwheel with Spitfire's tactical assesment already knew the weapon was unloaded and instead, questioned Frost Mane. Frost Mane exlained how Raiders slaughtered at the clinic were killed and is allowed to flee for his life by Cogwheel, much to the surprise and disapproval or Dust and Precious.
Forst Mane's whereabouts afterwards are unknown since he was heading in the opposite direction of Cogwheel and his friends.
The act of sparing Frost Mane has become a very risky subject to bring up in conversations as Cogwheel has discovered. Dust, Precious and Green Valley's sherrif, Radio.