We see Anya’s very old-fashioned apartment for the first time in The Replacement, and see it again in Into the Woods.

In The Replacement, Xander tells Willow to see how she handles it when she gets an evil twin. She says, “I handled it just fine”, a reference to when she met her vampire self in Doppelgängland.

The first episode to suggest that there was a problem with Joyce’s health was The Replacement when she told an arguing Buffy and Dawn that, “this must be my teenage daughter headache”. Joyce collapsed in Out of My Mind and was taken to the hospital where she was declared fit. …

When Willow bursts through Giles’ front door in The Replacement, Giles says, “I swear this time I know I had that locked.” We saw Spike come through the door in a similar manner in the episodes The Harsh Light of Day and The Yoko Factor.

Xander ‘convinces’ Willow in The Replacement that he is genuinely Xander by performing his Christmas Snoopy dance - first mentioned in Passion. Nicholas Brendon has performed this dance on numerous occassions for fans at conventions.

Spike gets a mannequin from the Sunnydale rubbish dump in The Replacement and later pretends it’s Buffy, a sure sign of his obsession with her. In Triangle he practises giving a speech and some chocolates to Buffy using the mannequin, to apologise for taking Buffy to see Riley at the …

We discover in The Replacement that Anya owns a gun, though we never see it again after that episode. Guns are usually frowned upon in the Buffyverse (seen in Phases, Homecoming, Flooded, As You Were and Touched), but it seems likely that Anya would have one.

In The Replacement, Xander wears an ‘Iowa’ t-shirt. Riley is from Iowa.

Michael Bailey Smith, who played the lava-headed Toth in The Replacement, has also appeared in Men in Black II, My Favorite Martian, The Fantastic Four, and A Nightmare On Elm Street: The Dream Child. He appeared in an episode of She Spies called ‘The Replacement‘ and played Belthazor in Charmed. …

The popular book series Harry Potter by J. K. Rowling is referenced a few times in Buffy. In Real Me, Dawn says, “I’m not going to Hogwarts”. This is a reference to Hogwarts is the school for wizards that Harry attends.
In Lessons, Willow wonders why Giles went “all Dumbledore …

Another vampire invitation rule is clarified in Real Me: only someone who lives in a residence can invite a vampire in. So, for example, Xander couldn’t invite a vampire in Buffy’s house.

The crazy guy who approaches Dawn in Real Me tells her “You don’t belong here”. We learn later in the season that crazy people can see Dawn for what she really is - a mystical ball of energy called the Key. The guy also says “curds and whey” which is …

In Real Me, we see that Giles has brought a new sporty red convertible BMW. This ties in well with his semi-mid-life crisis played out in season four. Being an unemployed librarian and ex-member of the Watcher’s Council must pay pretty well.

Bob Morrissey, who played the crazy guy who talks to Dawn in Real Me, played the same character in Spiral and The Weight of the World. He appeared as Dr. Gregson in the Angel episode ‘Heartthrob‘. He has also been in The Terminal, Northern Exposure and Soul Plane.

The song playing when Buffy and Riley play with a football on the beach in Buffy vs Dracula is ‘Finding Me’ by Vertical Horizon, from their album Everything You Want.