A British Werewolf in Danville is a 2011 Phineas and Ferb Gen Fic, written by a user/troper named FossilsDaDaDa, who also wrote First Contact a Gemini Story.

The story follows Phineas, Ferb, and his friends on Halloween night. In a true Phineas-andFerb fashion, Ferb is given , as they think, the coolest costume in history by being transformed by genetic engineering into a 200-pound green werewolf. Unfortunately, Ferb looses his mind shortly after Trick-or-Treating is over and begins to attack. Using Jessie's cleverness, Candace's strength, and Perry's venom, the gang tries to turn Ferb back to normal.

Its reviews have been almost universally positive, some even considering it one of the best fics ever written for the franchise.

• Action Dress Rip: Jessie tears the hem of her dress to run from the werewolf.
• Adults Are Useless: Major Monogram, literally the only adult who gets any screen time in this story, is the complete opposite of helpful.
• Becoming the Costume: One of the most literal examples in history.
• Big Badass Wolf: Were Ferb, once he looses his mind.
  • Silly fool, that's not how you spell
• Big Friendly Dog: Were Ferb, before he looses his mind.
• Big No: Phineas lets one out when
• Darker and Edgier
• Deadpan Snarker: Baljeet gets this gem:

• Death Glare: Baljeet receives one from Buford after questioning why he must look for costume supplies with him.
• Disney Death:
• Genre Savvy: Jessie is the only one who questions the rationality and safety of Ferb's costume. Phineas puts it out of her mind quickly, though.
• Girliness Upgrade: Jessie gets one, though according to her it's only because "It's a special night".
• Improbable Aiming Skills: Jessie's got 'em.
• Little No
• Mood Whiplash: Things go from perfectly happy to entirely terrifying for the characters quite abruptly in Chapter 4.
• Mutagenic Goo
• Noodle Incident: Okay, is there ever going to be a Halloween where I can trick or treat and not have to run for my life half the time?
  • Which, after the canon episode "That's the Spirit", kinda makes sense.
• The Only One Allowed to Defeat You: When Candace protected Phineas from Ferb as a Werewolf.

• Original Character: Jessie, Ferb's twin sister.
• Our Werewolves Are Different: And how...
• Painful Transformation: Turning into a Werewolf doesn't seem to hurt, but turning into a deadly, bloodthirsty one does.
• She Cleans Up Nicely: Jessie's change into her Repunzel costume is described like this.
• Shout-Out: Several:
  • For starters, the very title is a Shout-Out to a famous werewolf movie.
  • As is the title of chapter seven.
  • "She's still got her smeet."
  • Buford, if I live, I am going to kill you.
• Tempting Fate: Oh man, they were just begging for Ferb's costume to go wrong...
• The Mind Is a Plaything of the Body: Doesn't happen immediately, but yes.
• Too Dumb To Ensure The Survival Of Seven Innocent Children: Major Monogram. He is no help at all in taking care of the werewolves.
• Twin Telepathy: Ferb and Jessie. Justified by the fact that they have alien blood in their family.
• What Could Possibly Go Wrong?: It's the title of Chapter 2.