Unlike Oracles, Seers can see into the future without the help of crystal balls. The first Seer also once said that she predicted further into the future and more accurately than the oracle, hinting that Seers are more powerful than Oracles.
The Crone: Although not using the title, she is considered a Seer. She was a well respected advisor to powerful evil demons and a powerful demon herself. She was interested in Wyatt Halliwell because of his tremendous power.
Kyra: The second demon known as the Seer. She had information on Avatars and wanted to become mortal, as she resented her demonic life.
Alexi: A close friend of Cole Turner in the past. Cole came to her in the hope that she will help him find Prue Halliwell, whose spirit had gone missing.
Notes and Trivia
Seer is considered a title, not a species of demon, due to the fact that each Seer possessed distinctly different powers, hinting they are not related by any means.
Each Seer also had vastly different goals and motivations.
All known Seers were vanquished over the course of the series.
Kyra was brought forward in time before she could be vanquished by Prue in the comics.
All of the Seers that appeared in the television series had a production still taken of them.
Seers appeared in a total of 13 episodes throughout the course of the tv series; and 6 issues of the comic.