Derpy Hooves lives an average life with an average room-mate and an average daughter. She makes her life as a mail-mare. One fateful night, the sun doesn't rise, and equestria's threatened by Nightmare Moon. Derpy soon realizes the fate of every-pony she's cared for lays in her (and a few other's) hooves. Now if only she can wrap her head around that Doctor fellow…
Cross-over if you count the doctor.