Patty Halliwell (Charmed)

 Patty Halliwell, charmed ones’ mother has appeared on several episodes, both in flashbacks when she was alive and when she was a spirit ( after her death).

Patty Halliwell appeared in at least one episode of every season, with the exception of the sixth season which is the only season where Patty Halliwell’s character doesn't appear, due to Finola Hughes ( the actress who portrays the mother of Charmed ones, wasn't available to reprise her role back then). In fact the 11th episode of the sixth season “Witchstock” was planned to be focused on Patty Halliwell's youth, but due to unavailability of Finola Hughes for the role, the writers had to rewrite the story and focused on Charmed ones’ grandmother Penny, which led to certain plot inconsistencies and continuity mistakes.

The first appearance of Patty Halliwell in the show was on the third episode of the first season “Thank you for not morphing”, when she was seen in a homemade video tape playing with her daughters when they were little children and was portrayed by Alyssa Milano, the actress who portrayed Phoebe ( back then they were the early episodes and the writers hadn't established the stories of secondary characters well defined). On the 13th episode of the first season “From fear to eternity” Patty Halliwell’s character was portrayed by an unknown actress.

And finally from the 17th episode of the first season “That 70’s episode” onwards Patty Halliwell’s character was portrayed by Finola Hughes.

As an additional fact the character of Patty Halliwell didn't show her active powers when it was seen on the TV series as a spirit unlike her mother Penny that she openly showed her active powers characterised as a spirit.