A concept we've been wanting to get out of our head for a while now! We have some plural pony headcannons, and were going to do a series of the ponies we think are plural! The way our headcannon works is that unless a headmate is WILDLY different from their system (or in some cases, ostracized, in Equalight's case), they will have one part of their name that they share as their system name! So in this case, Starlight's system is the Starlight system! So we have Starlight Glimmer, Starlight Flicker, and Starlight Gloomer! ^^

Glimmer is the host, and has been there since forever. During the "Our Town" years, glimmer saw very little time fronting, usually only at night. Her encounter with Twilight Sparkle and the Mane Six led to her "waking up", which resulted in a season-long fight between the two headmates that led to Equalight modifying Starswirl's Time Scroll and struggling to maintain her power the system. Equalight was defeated by Glimmer when she learned how to take accountability for her actions through Twilight's help, and became the Princess of Friendship's pupil.

Equalight is the second oldest alter, next to Glimmer. She was cracked when Sunburst left for magic school, and grew in power and resentment as other ponies noticed her system's irregularities. She actively harms the others whenever she feels like they're speaking out, and has a lot of negative ticks picked up from her dad.
While Equalight is in "permanent" detention, after season 9, when Starlight fights Crysalis, we headcannon that Starlight lets Equalight switch in because she has the most power out of all of them! Meaning, that after the events of FiM, Equalight is allowed to front again, though only during school breaks. ^^

Flicker is the trauma part holder of the overbearing nature of her father's parenting style, and the loneliness she felt as a filly. Flicker is the second most frequent headmate, fronting usually when she becomes overwhelmed by negative emotions to the point of breaking down to a filly-like state, or whenever she and Gloomer are allowed to co-front as a part of "scheduled age regression" days.

Gloomer is their system's teen alter, and also their resident protector. While she usually stays back in headspace, she's always around whenever Flicker is because her job is mostly to protect and soak up the negative energy that would otherwise be thrown towards Flicker. She and Equalight

Next up is Pinkie Pie!