A few flashback scenes from Buffy the Vampire Slayer are seen in the opening episode of Angel - ‘City Of…‘ - whilst Doyle is telling Angel the story of his life:
Doyle: “Once upon a time there was a vampire. And he was the meanest vampire in all the land.” (Flashback to Angel biting Daniel and Margaret in Amends and the girl in the alley in Innocence). “All the other vampires were afraid of him, he was such a - bastard. Then one day he’s cursed – by gypsies.” (Flashback to the gypsy lady speaking the curse in Becoming, Part 1) “They restore his human soul. And all of a sudden he is mad with guilt. You know: ‘What have I done?’ You know, he’s freaked.”
Angel: “Oh, okay, now I’m sleepy”
Doyle: “Yeah, well, it’s a fairly dull tale. It needs a little sex, is my feeling. So sure enough: enter the girl.” (Flash to scenes of Buffy from Anne) “Pretty little blonde thing, vampire Slayer by trade. And our vampire falls madly in love with her.” (Flash to Angel and Buffy kissing in Revelations) “Eventually the two of them, - well, they get fleshy with one another. Well, I guess the technical term is perfect happiness. But when our boy gets there…” (Flash to dream sequence form Amends) “he goes bad again. He kills again. It’s ugly. So when he gets his soul back for the second time, he figures hey, he can’t be any where near Miss Young Puppy Eyes without endangering them both. So what does he do? He takes off.” (Flash to Angel walking away in Graduation Day, Part 2) “Goes to LA. To fight evil - and atone for his crimes. He’s a shadow, - a faceless champion of the hapless human race. – Say you wouldn’t have a beer of any kind in here, would you?”