The House Call (3 of 4-ish)
Twilight: Zecora hasn't been giving Rainbow Dash anything unusual. Just a minor magical concoction to ward off common pony ailments.
Housecall: Which might be remotely interesting if herb witches could perform magic.
Twilight: Doctor Housecall, Zecora's brews aren't Pony Magic, but they are magic. They've helped me out dozens of times.
Housecall: You think they've helped you out. What they really did was give you a nice warm fuzzy feeling so that your actual Pony Magic could do its work. There are only two kinds of magic in this world: Pony Magic, and magic from shiny magic rocks. Which is kind of a coincidence, because we're about to use one to knock out the other.
Twilight (narrowing her eyes): What are you talking about, Doctor Housecall?
Housecall: Here's a hint. It starts with "An-" and ends in "-Timagicspell."
Twilight: An anti-magic spell?
Housecall: Wow! Guess those brains aren't just for show. You're a perky little wizard prodigy, I need you to hit our patient with something that'll get rid of her little shiny rock curse.
Housecall (turning around): Did you hear that noise? Sounded kind of like an uppity purple unicorn questioning my judgment.
Twilight: THAT'S BECAUSE IT WAS AN UPPITY PURPLE UNICORN QUESTIONING YOUR JUDGMENT! Well, maybe not "uppity". The point is, you were wrong about it being hot sauce. How is your shiny rock idea any different?
Housecall: For the sake of argument, WHO CARES? Just cast the spell!
Twilight: An anti-magic spell isn't just any spell, Doctor Housecall! It's not like undoing a spell you know. It's unraveling the fabric of magic itself! Princess Celestia warned me about attempting spells like this!
Housecall: Right, and magic equals friendship, so you're slapping that in the face too. I get it. It's good to know you care more about your wizard ethics than you do about the patient.
Twilight (dubious): I want to ask Princess Celestia.
Housecall: Takes the burden off of you, because you know she'll say "no".
Twilight: Then I won't do it.
Housecall: And our patient misses the Latesummer's Eve Art Show. Or worse! You're a terrible Pony Magician!
[Housecall softens slightly at Twilight's reaction to this.]
Housecall: Listen. Celestia cares about making our patient better. This spell you're going to cast will make our patient better. Celestia'll be so thrilled she won't even care how the patient got that way.
Twilight: Not telling Princess Celestia something important that she deserves to know is just like lying to her, Doctor Housecall. And the Princess isn't just my teacher, she's my friend. Friends don't lie!
Housecall: Everypony lies.
[Twilight and Housecall stare at each other in a contest of wills for a moment. Then, without breaking eye contact, Twilight calls out.]
[Spike zips into the scene.]
Spike: What is it? Is the patient feeling better? Can we do the funny burp spell now?
Twilight (eyes still locked on Housecall): Spike, take a letter. I need to ask Princess Celestia's permission to cast an anti-magic spell on Rainbow Dash.
[Housecall rolls his eyes as the scene dissolves to...]
* * *
[Princess Celestia's study. She is writing a letter using quill-and-telekinesis. We can hear her voice as she writes.]
Princess Celestia: Dear Twilight Sparkle: You know that I have the utmost faith in your abilities and your discretion. That having been said, the spell you're asking about is very difficult and dangerous magic. Still…
[Dissolve to the library. Twilight is reading the letter.]
Twilight: Still, if you and Doctor Housecall truly believe that this is the best way to help your friend Rainbow Dash, you have my blessing. Signed, Princess Celestia.
Housecall: Happy now?
[Twilight trots grimly over to the increasingly green-looking Rainbow Dash.]
Twilight: Oh, Rainbow Dash. I hope this helps.
[Twilight closes her eyes, and with a considerable effort of will, summons a cloud of inky-looking energy which twines and settles around Rainbow Dash before fading. Rainbow Dash's eyelids flutter.]
Rainbow Dash: Wha…?
Twilight: Rainbow Dash! How are you feeling?
Rainbow Dash: Not… not good. Really bad. What did you guys do t--
[Rainbow Dash's eyes go derpy and she collapses back to the bed, shivering.]
Twilight: Rainbow Dash! RAINBOW DASH!!!
[Cut to commercials.]
* * *
[Later, in the Library's lower room. The blackboard has been transported downstairs and all the non-Rainbow Dash ponies are present again, plus Chase. "Red Trail" has been crossed off on the blackboard and "The Shakes", "Derpy Eyes" and "Sensitivity to Antimagic" have been added to it.]
Twilight: Our spell didn't make Rainbow Dash better. It made her worse! I told you we shouldn't have dabbled in anti-magic!
Housecall (tapping his head with the top of his cane): Nice to know you're going to waste what little time we have left being self-righteous. The art show's in a few hours. I need input, people. Chase!
Chase: I'm sticking with diet.
Housecall: Doesn't explain her reaction to the antimagic, and useless unless we know what she ate. Princess!
Rarity: I've had quite enough of this treatment and shan't subject myself to further humiliation. Hmph!
Housecall: Useless and annoying. Applejack!
Applejack: Well, I tell y'all, I dunno what's wrong with R.D., but I ain't never heard of no kinda sickness that enough apples wouldn't 'ventually cure.
Housecall: Useless, annoying, and shockingly dumb. Fluttershy!
[Fluttershy squeaks at Housecall's angry demeanor and says nothing.]
Housecall: And we're back to just plain useless. Pinkie Pie!
Pinkie Pie (joyfully poinging up and down): It's lupus!
Housecall: It's not lupus.
Pinkie Pie: Aww.
Housecall (rounding on Twilight): That just leaves you, Brainy Smurf. You were right about the anti-magic spell, fine. What is wrong with the patient?
Twilight: I don't know! If I did know, I'd have cured her already! But what I do know is that she isn't "the patient". She's my good friend Rainbow Dash. And you haven't even called her by her name once!
Housecall (angry): Calling her by her name ISN'T GOING TO FIX HER.
Twilight: Maybe not. But if Rainbow Dash misses the art competition, she's going to be very, very sad. And she's going to need friends around to help her bounce back. Friends who care about her, not just what she's sick with! And you are not that friend, Doctor Housecall, because you don't care about ANYPONY!
[Housecall glares at Twilight, frowning angrily. Then he hobbles to the door.]
Housecall: Fine. Go ahead. Treat the patient with massive doses of caring. See how far that gets you. I'm going out for a drink.
Chase (startled, helpless): But what do we give her for medicine?
Housecall: Do you have saddle wax in your ears? CARING. That's all any of you are interested in, aside, apparently, from failing miserably. When caring doesn't work, start treating for illnesses randomly. You might just hit something.
[Housecall exits, slamming the door behind him. The ponies, and Chase, are left stunned by his departure, staring at the door.]
Applejack: Well, golly.