Bad eyes

This line of the vampire Marissa was cut from Deep Down due to length:

“I didn’t see nothing. I swear. You know how dark it is down by the bluffs? And hey, my eyes were never that good. Sure, the creature of the night thing helps, but….”

Noel Gugliemi

Noel Gugliemi, who played Vince in Life Serial, also played “Driver Vamp” in the Angel episode ‘Deep Down‘. He can also be seen in Duck, Party Animalz, Wrong Turn (starring Eliza Dushku), S.W.A.T., Bruce Almighty, Old School, Training Day, The Fast and the Furious, The Animal, Price of Glory (as Angel), 24 and The X Files.

Justine Cooper

Justine’s twin sister Julia was killed by vampires, leaving her to seek vengeance for her loss. She was recruited by Holtz in his war against Angel, and became his right-hand woman, though he treated her roughly. Utterly devoted to Holtz, Justine aided him to kidnap Connor, even slitting Wesley’s throat in the process. She was devastated when Holtz escaped to a hell dimension with Connor without her, but aided him when he returned an old man. On his request she killed Holtz, making it look like a vampire bite, to set up Angel. She helped Connor to send his father to the bottom of the sea, but Wesley forced her to help him to find the vampire.

Getting perspective

Angel says to Connor in Deep Down, “What you did to me - was unbelievable, Connor. - But then I got stuck in a hell dimension by my girlfriend one time for a hundred years, so three months under the ocean actually gave me perspective.” He’s referring to the Buffy episode Becoming (Part 2), in which Buffy was forced to send him to hell in order to save the world.

Toasting family

The scene of Connor’s happy new life in Home, in which he toasts his new family, is similar to the dream Angel had when he was underwater in Deep Down. The life Connor has now is the life Angel wanted for himself, his son and his colleagues.

Conan

When he’s trying to get Andrew to kill the pig in Never Leave Me, Warren/The First says, “You’re Conan. You’re the destroyer. It’s you against nature.” This is a reference to the 1984 movie Conan the Destroyer, which starred Arnold Schwarzenegger. The movie was the sequel to Conan the Barbarian (1982).
In Deep Down, Gunn says of Connor, “His nickname back in Quor-toth was ‘The Destroyer,’ and unless you put ‘Conan’ in front of that I’m guessing it’s not a good sign.”

Evil Dead

Sam Raimi’s Evil Dead trilogy, starring Bruce Campbell, is alluded to a few times in Buffy. In Amends, the First screams, “Dead by sunrise”, which could be a nod to the subtitle of Evil Dead 2, namely, “Dead by Dawn”. In Crush, Xander says to Spike, “Hey evil dead you’re in my seat”. In Conversations with Dead People, Buffy says, “Yeah, what I really need is emotional therapy from the evil dead.” In Deep Down, Gunn says, “Evil Dead was probably just messing with us.”
The scene in Restless in which Xander is being pursued by the first Slayer down a long corridor (eventually leading to his parents’ basement) is highly reminiscent of a similar scene in The Evil Dead, in which Ash (Bruce Campbell) is being chased by the entity. Another visual reference to Evil Dead can be seen in After Life. The scene in which Anya become possessed is similar to a scene in the movie in which Linda (Ash’s girlfriend) gets possessed by evil spirits.
Sam Raimi was executive producer of Sarah Michelle Gellar’s hit movie The Grudge.

M. C. Escher

In Deep Down, Angel says, “…three months under the ocean actually gave me perspective. Kind of a M. C. Esher perspective - but I did get time to think.” Maurits Cornelis Escher (1898 – 1972) was a Dutch graphic artist known for his mathematically inspired, seemingly impossibly constructed works such as Relativity and Waterfall, as well as his Metamorphosis works.

Miracle-Ear

In Deep Down, Lorne says “Not a peep. But if I Miracle-Ear anything I’ll send up a smoke signal.” He’s referring to the hearing aid that is advertised as being so small it’s almost invisible.

Moby Dick

Xander dresses as a pirate in All the Way. Giles calls him “Ahab” after the captain in the novel Moby Dick by Herman Melville. In Deep Down, Gunn says that Wesley has “been playing a little Ahab”.

Pippin

In Deep Down, Linwood tells Lilah, “This is my corner of the sky”. This is an in-joke as John Rubenstein (who plays Linwood) starred in the original Broadway production of the musical Pippin, in which one of the songs he sang was titled ‘Corner of the Sky’.