Replying...
Intro. Shimmy Shake and Lighthoof are relatively secondary characters in "My Little Pony: The Magic of Friendship", so they do not have a "background story" or complex argumentary arches such as the main characters. Its relevance focuses mainly on a key episode: His debut and history in "2, 4, 6, Greaaat" (Season 9, Episode 15): This episode is where Shimmy Shake and Lighthoof have their greatest prominence. The main plot involves the School of Friendship forming a "Buckball" team (a sport similar to basketball) and Twilight Sparkle puts Rainbow Dash in charge of the Porristas team. Shimmy Shake and Lighthoof are presented as the "main dancers" of the Porristas squad of the Friendship School. They prove to be very talented and dedicated to choreography. However, the rest of the Porristas team is quite inept and its captain (MANGOOD) is apathetic and demotivated.

Shimmy Shake and Lighthoof

@Blue Glow