Amends

In which Angel, suffering from the Flashbacks of Doom, decides that the examined life is not worth living.

Official back-of-box synopsis:

The Christmas spirit is dead in Sunnydale. Buffy, Giles and the gang's research into why Angel has been sent back to Earth leads them to 'the First Evil' and the first snow Sunnydale has ever seen. Meanwhile, Willow and Oz decide to give their relationship another shot.

From the old WB Buffy website:

THE GHOSTS OF CHRISTMAS PAST - As Buffy and her friends make plans for a quiet Christmas vacation, Angel is haunted by visions of his violent, demonic past, including the ghost of Jenny Calendar. Meanwhile, Willow goes to great, seductive lengths to try to convince Oz that he is the one for her; and Xander painfully adjusts to his life without Cordelia. Joss Whedon wrote and directed the episode.

Cross-reference:

episodes featuring Symbolic Weather:

• Surprise
  There's a raging thunderstorm as Angel turns to Angelus
• Conversations With Dead People
  a very localised storm, and The First, strike 1630 Revello
• this episode
  A Snow Day in California = message that Angel shouldn't kill himself

episodes where the Mutant Enemy guy is different:

• Becoming (part 2)
  he "needs a hug"
• Graduation Day (part 2)
  he wears a mortar-board hat
• Once More, With Feeling
  he sings "grr-arrgh" (it's Joss' voice)
• Storyteller
  The "we are as gods" one.
• Chosen
  He turns to the camera for a moment
• this episode
  wears a Christmas hat

Cast:

• Sarah Michelle Gellar as Buffy
• Alyson Hannigan as Willow
• Nicholas Brendon as Xander
  

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• Anthony Stewart Head as Giles
• Charisma Carpenter as Cordelia
• David Boreanaz as Angel
• Kristine Sutherland as Joyce
• Robia Lamorte as Jenny Calendar / The First
• Seth Green as Oz
• Saverio Guerra as Willy
• Eliza Dushku as Faith
• Shane Barach as Daniel / The First
• Edward Edwards as Male Ghost / The First
• Cornelia Hayes O'Herlihy as Margaret / The First
• Mark Kriski as Weatherman
• Tom Michael Bailey as Christmas Tree Guy