Umbrum

Umbrum, also known as shadow ponies are a race of malevolent beings. Creatures of monsterous appearance, Umbrum are beings of pure evil who wish to do nothing but manipulate others and conqueror foreign kingdoms.

Biology
Umbrum appear to be immortal, or at least have absurd lifespans, as Rabia is apparently well-over 1,000 years old. This may, however, be in part due to how time works in their dimension, as Radiant Hope lived within it for over 1,000 years without apparently aging a day. Umbrum's bodies appear to be non-corporeal and smoke-like. They have little control over their bodily appearance however, and change from from a fairy-like pony appearance that lured in Radiant to what can only be assumed to be their true forms; a more monstrous, barely equine looking monster when they were met with Love magic. Being from a world of darkness, Umbrum are weak to strong sources of light, allowing for even weaker unicorns such as Cookie Crumbles to be capable of fighting them off.

Behavior
Manipulative and cruel beings, Umbrum are very violent, but also very intelligent. They also appear to have extreme patience and memory, allowing a plan to go on for over 1,000 years, which involved tricking and befriend Radiant Hope for all those years. They apparently find love and pony magic to be disgusting.

History
Over a thousand years ago, and her fledgling empire encountered the Umbrum deep in the Crystal Empire and were disgusted by the sight. Even the brutal and tyrannical Chrysalis feared the Umbrum as being far to destructive, wicked and evil, burning homes and ruining the lives of the ponies who lived there. At some point, they were banished away to an alternate dimension of pure darkness by Princess Amore. A portal to their dimension was located not to far away from the Crystal Empire. Eventually, during the Amore dynasty period, the Umbrum created a unicorn-like offspring who they named "Sombra" in order to infiltrate the Crystal Empire. Indeed, the Crystal Empire took in the lost foal and raised him in a local orphanage where would call home.

However, Sombra was not the savior they wanted and instead he ruled the land himself, shattering Amore and locking away the Crystal Empire in a timewarp for over a thousand years. In this time, Radiant Hope migrated to the Umbrum dimension and seemingly became friends with them. However, after a thousand years and the Crystal Empire was once again under Sombra's control, Radiant Hope and ventured into the Umbrum dimension only to find the Umbrum in their true forms. Soon after wards, when Twilight Sparkle wounded Radiant in a crossfire, an angry Sombra proclaimed himself to be the "king of the monsters" and unleashed an army of Umbrum upon the Crystal Empire.

With the combined forces of several civilians from Ponyville and some (minor) assistance from, the Mane Six attempted to beat the Umbrum back. Ultimately, however, it would be Sombra who brought an end to their reign of terror once he realized that he could choose a destiny for himself. He promptly restored the Crystal Heart, exiling the Umbrum back to their prison, and was himself transformed into a full.

Appearances

 * "The Siege of the Crystal Empire"
 * "The Siege of the Crystal Empire"
 * "The Siege of the Crystal Empire"
 * "The Siege of the Crystal Empire"
 * "The Siege of the Crystal Empire"
 * "The Siege of the Crystal Empire"