The Tantabus is an amorphous blob of magical energy that draws magical power from the dreams of those it "infects". While in this dream realm it has to power to know a pony's fear and use that against them as well as the ability to manipulate its own form and with enough power the ability to traverse the dream realm into the dreams of other ponies it has seen within the dream realm.

The Tantabus was the creation of Princess Luna and was created as a form of self-punishment for the damage she had caused during her time as Nightmare Moon. The Tantabus resided in Princess Luna's dreams and nightly came to torment her with visions of her worst fears. However Princess Luna's friendship with the Mane Six led to her having one dream in which the Mane Six came and fought the Tantabus on her behalf, having learned of them through this dream and having gathered enough power to break from Luna's dream the Tantabus was able to spread to the dreams of the other six ponies. Through their dreams the Tantabus gained more power and eventually was able to infect the dreams of all of Ponyville. Princess Luna used her power to confine the Tantabus to a single shared dream among all of Ponyville where the inhabitants battled fiercely against the creature as it tried to escape. However it soon became clear that the Tantabus drew its power from Luna's guilt and self-loathing and only became stronger when Luna realized she had once again been responsible for harming the inhabitants of Equestria.

The Mane Six absolved Luna of her previous wrong doings and pleaded that she do the same for herself. Realizing that this was the only way to stop the Tantabus and understanding that her past mistakes did not have to lead to future ones Princess Luna was able to absorb the Tantabus into herself. She would never forget her past mistakes, but she would use its power to prevent future mistakes from then on.

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