The Shadow Realm

The Shadow Realm (not to be confused with the Void) is a location in the Saturnverse.

Appearance
The Shadow Realm is an exact replica of the real world that is cast in a dark blue-black color. Everything and everyone that dwells there is a perfect shadowy replica of the real version however they are also perfect in every possible way, making anyone banished there feel inadequate by comparison. There is no exit from the Shadow Realm, if you are banished there you can only escape if someone in the real world brings you back through a portal.

History
The Shadow Realm was mentioned as early as Chapter 2 of the manga but was not seen until Princess Luna was banished to it in the episode "Dark Blue Moon". Later many minor villains would also be banished as well as a few allies.

List of those Banished

 * Princess Luna
 * A toilet bowl cleaner
 * Saturn's prised map of the Elder Scrolls V Skyrim
 * Sans Undertale (Escaped within 5 minutes. Method of escape unknown)
 * Three teenage Homestuck cosplayers
 * Two arms belonging to an African man

Trivia

 * The author of the Saturn series made the Shadow Realm in response to people who wrote his characters as perfect versions of themselves in fanfiction.
 * Sans stated once that all food in the Shadow Realm tastes like "Goop"