Fallout: Equestria - Old Souls is a sidestory written by Amethyst Wind. The story follows Snowflake as she traverses the far north Equestrian Wasteland after being unwillingly evicted from her Stable. It is set in and around Equestria's northern border.
The plot focuses around Snowflake, a unicorn Stable filly, as she works to find her way after being evicted from her home in Stable 61. She now has to deal with the terrifying reality of being exposed to Old Equestria's influence and the dangers of the Wasteland, including Raiders, slavers, Rangers, and other dangers.
Fallout: Equestria - Red Eye, DJ Pon3 and the war are all referenced. Old Souls is set far to the north so there isn't much overlap. All Fallout: Equestria canon is applied to Old Souls.
Heroes - Dise and Caledonia are mentioned during a visit to the Whitepony records archive facility. Bosco claims to have never heard of them.
Rangers of Wintertrot - Wintertrot is mentioned during a visit to the Whitepony records archive facility. Bosco claims to have never heard of it.