|The world was breaking, shattering. Gray bands of ash flew past me, a part of me, an extension and an embodiment all at once. The color was drained from my eyes, replaced instead by a white flash of light.|
|- Eljunbyro ch. 3|
Sequencing (more precisely Sphere Sequencing Technology) is a mana-driven, scientific process in which a unicorn may experience the memories of another pony, living or dead. The technology was apparently developed by scientists working for the council of Ledomare, after which the technology was stolen by Garnet and replicated by Nightshade Industries. Sequencing is first encountered in the early chapters of Eljunbyro, as Bellesmith is vicariously experiencing the memories of Rainbow Dash. Later on, it is shown to be used with the remains of ancient pegasi to glean knowledge from their memories. Madame Nightshade also employs it as a form of psychological torture.
For sequencing to be possible, the unicorn must have a broken horn, and is therefore unable to perform regular magic. Belle, when describing her future in Val Roa, speaks of developing a "safe" way for sequencing which does not require such harm.