Background Pony #037B
I used to head-canon that Sunny’s mom was probably some kind of archeologist who liked to go out on expeditions to seek answers from the past (to contrast with Argyle who seemed content to stay home and study his personal collection of ancient artifacts and documents), and ultimately went missing on one of those expeditions and has not been heard from since then.
I’m actually quite pleased to see just how close my head-canon came to matching the true canon we got to see here.