Sailor Moon

Sailor Moon is a long running animanga franchise that began in 1991 and is still in production to this day in some form. There are three constants in this world: Death, Taxes, and Sailor Moon anime. Often compared to Dragon Ball in terms of prolificness and iconicness, Sailor Moon is an extremely iconic series in its own right. Being a show aimed at female audiences, Sailor Moon has had a number of references in My Little Pony.

Friendship is Magic

 * Luna Eclipsed: Ponies dressed as Usagi Tsukino and Makoto Kino were seen during "Nightmare Night".
 * Scare Master: Fluttershy drew artwork of Usagi

Better Together

 * Queen of Clubs: cosplayed as Tuxedo Mask as the rest of the Anime club performed the Sailor Senshi pose.

Nightmare Rarity

 * Nightmare Rarity - Chapter I: Usagi and Makoto were seen buying food in Ponyville.

Characters
The following characters are directly based off Sailor Moon characters.
 * Aqua Mist
 * Burning Heart
 * Celena
 * Charon
 * Juno
 * Larissa
 * Love Melody
 * Natural Satellite
 * Saturnalia
 * Umbriel

Other connections

 * Debora Magnaghi, the Italian voice for Maud Pie and Adagio Dazzle provided the voice for the Italian dub version of Sailor Mercury.
 * Nigela Ruka, the Albanian voice for Applejack provided the voice for the Albanian dub version of Sailor Mars.
 * Eneida Rabdishta, the Albanian voice for Sweetie Belle provided the voice for the Albanian dub version of Sailor Venus.
 * Gerona Karabashi, the Albanian voice for Scootaloo provided the voice for the Albanian dub version of Sailor Chibi Moon.
 * Xhesika Kasemi, the Albanian voice for Babs Seed provided the voice for the Albanian dub version of Sailor Mercury.
 * Noa Kashpitzki, a prolific Hebrew voice actress provided the voice for the Hebrew dub version of Sailor Jupiter.
 * Rocío Garcel, a Mexician voice actress provided the voice for the Mexican dub version of Luna.