John O’Leary, who played one of the Watchers in Checkpoint, also appeared as ‘Kaltenbach’ in the season six Buffy episode All the Way.

Kris Iyer, who played Watcher Nigel in Checkpoint, has been in The West Wing, CSI, Philly, Becker, Boy Meets World, Diagnosis Murder, NYPD Blue, JAG, Babylon 5 and Sliders.

Oliver Muirhead, who played the Watcher Phillip in Checkpoint and Never Leave Me, has also appeared in Friends (as the Jeweller in ‘The One With The Ring‘), Seinfeld (as Lubeck in ‘The Frogger’), Suddenly Susan, Unhappily Ever After, Step by Step, Smart Guy, Lois & Clark: The New Adventures of …

Cynthia Lamontagne, who played the Watcher Lydia in Checkpoint and Never Leave Me, played a Fembot in Austin Powers: International Man of Mystery, which also starred Seth Green. She has also appeared in The Drew Carey Show, That ’70s Show (as Rhonda), Crossing Jordan, Frasier, Dharma & Greg, Mad About …

Spike is obsessed with an onion flower served at the Bronze, which he mentions on several occasions. In Triangle, he says to Xander, “They have chicken wings, too. Also, a sort of a flower-shaped thing they make from an onion. It’s brilliant.” In Crush, he says to Buffy, “Especially since …

We hear ‘There’s No Other Way’ by Blur in the Bronze in Triangle, as Xander and Spike are talking.

In Triangle, Willow uses salamander eyes in her ball of sunshine spell, which cost $10 for twelve. These were last mentioned in Out of My Mind, when Giles said, “No, these are salamander eyes, it’s the cataracts which give them their newt-like appearance. They’re really equally effective, though, it’s just …

In Triangle, Anya reminds Willow that D’Hoffryn offered her a job as a vengeance demon, which occurred in Something Blue.

Xander’s wrist is broken by Olaf in Triangle and he wears a sling in Checkpoint. It was previously broken in Becoming (Part 1). His girlfriend Anya’s shoulder was dislocated in Real Me and she wore a sling in The Replacement. Olaf also continuously beat Xander with his hammer, which was …

In Triangle, Anya mentions that she knows Willow broke up Xander and Cordelia by kissing Xander (in Lover’s Walk). It was this act which summoned Anya as a vengeance demon to Sunnydale, and which led to her being made mortal again.

In Triangle, Willow mentions she’s still trying to “de-rat Amy”. Amy was a witch who turned herself into a rat to escape persecution in Gingerbread. Amy finally becomes human again in Smashed.

In Triangle, Dawn asks Buffy what she’s doing and the Slayer replies, “playing soccer”. When Dawn asked Buffy what she is doing in Real Me, she got the answer “my boyfriend”.

Giles goes to England to talk to the Watcher’s Council about Glory in Triangle, which leads to a visit by them in Checkpoint. Giles was sacked by the Council in Helpless, and Buffy resigned from working for them in Graduation Day (Part 2).

In Into the Woods, Xander says to Buffy about Riley, “Dependable? What is he? State Farm?” State Farm is an American insurance company.

In Into the Woods, Riley says to Buffy, “I wanted to even the score after you let Dracula bite you.” This occurred in the episode Buffy vs Dracula.