Agent Doyle:
Debut -- Invisible Girl (Season 1)
Last Seen -- Same Episode
Agent Doyle's a "man in black" -- well, sort of. I didn't see that movie, after all. Anyhoo, he and his partner are loitering near the trees outside of school. Willow first notices them on the schoolgrounds while Cordelia's making her May Queen acceptance speech. She offhandedly asks Buffy if Cordy's hired a bodyguard.
Later, the two burst into the Bronze to take Marcie Ross away so they can "rehabilitate" -- read, "re-educate" -- her. Neither agent gives Buffy much info., and Doyle is particularly odd, in my opinion.
Why I Think Doyle's Odd:
"Oh...have a nice day." -- to Buffy and possibly Cordelia. He turns back to say this after he's already started to leave. Weirdness.
He's no Mulder. Heck, he's not even Scully!
Agent Manetti:
Debut -- Invisible Girl (Season 1)
Last Seen -- Same Episode
He's...Agent Doyle's partner! And he's no Mulder, either! He introduced himself and Doyle to Buffy and Cordy, and told Buffy that instead of curing Marcie, they could rehabilitate her into becoming a useful member of society, "..very useful." Later we see him and his partner escorting the unseen girl to a class on espionage, infiltration, that type of thing. Like we really need more of that in our society, eh, guys? Thanks a bunch, feds.
Doyle and Manetti have the dubious honor of appearing in one of my least-fave episodes.
The ABCs of Sunnydale