Rarity got her key after realizing the true meaning of Generosity.  
Rainbow Dash got her key when she learned that she should be loyal to her friends  
Pinkie Pie realized that RD didnt enjoy the Goof Off and was sad, so since she was The Elemnt Of Laughter, she quit so that Rainbow Dash would be happy.  
Fluttershy Learned that Kindness comes in many forms.  
Applejack will probably learn something about speaking your mind, or will teach FLim and Flam the value of Honesty.

@PonyPon  
Applejack may do some spying on Flim and Flam or it may not even concern Applejack at all! What if The title is so called because Granny Smith decides to live life to the fullest and Jump on A Cliff that may change everything?

@Background Pony #DFBC There’s more to the series than Ponyville you rube. (although sometimes it seems the writers forget that too. They must need more ‘nudging’)

@Background Pony #3A6F  
What of their Rainbow Eyes moments?

@Background Pony #3A6F  
This is my conclusion as well.

4x08 - Rarity gets a spool from Coco for teaching her about generosity  
4x10 - Dash gets a badge from Spitfire for teaching her about loyalty  
4x12 - Pinkie gets a chikun from Cheese for teaching him about laughter  
4x16 - Fluttershy gets a flower from Seebreezie for teaching him about kindness  
So in 4x20 AJ will teach Flim and Flam about being honest?

@Niggoslav_Krawczyk  
I don’t care about Gilda, she never made an impression on me. And who normally returns to a town that they were chased off from?

@Serris And yet still no return of Gilda ;_;

I fail to see how can they possibly work in a lying on purpose AJ in an episode like that. Since Fluttershy wasn’t unkind, I don’t think AJ would be dishonest.

@PonyPon  
What? Choosing not to choose, and messing up the Goof Off. That’s not being the opposite of royalty and laughter. Only their discorded selves were the opposite of their elements. Being loyal to another team is still loyalty, and Pinkie having a teporary conflct is not giving up on parties.

@Serris  
Flim and Flam were some of my favorite one-time characters. If it’s handled right this will be a great episode.

I definitely have a feeling this will be Applejack’s key episode

@PonyPon  
And Rarity?

@Background Pony #DFBC  
What about Dash and Pinkie?

@Krek  
Was Fluttershy unkind in her key episode, no she wasn’t, and AJ will not be dishonest in her key episode. The key episodes are about teaching someone else the element and receiving a key in return. It has nothing to do with the mane six being the opposite of their elements, which they never were in their respective key episodes.

@Dashy  
That would be interesting.
 
And Aj might be so against that, so unwilling to see the truth, that she switches out their tonic for turnip juice or something to try and prove its ineffectiveness…

I thought… Maybe Flim&Flam improved at making their stuff and it is actually good, but AJ refuse to admit it because of they did before?

Of all the characters… They bring those two again…  
I almost don’t want to watch the episode…
 
Nah. I’ll see what happens.

@Grieffon  
That is most likely the situation. The top right corner box implies that she get’s worse right after she takes it

@Grieffon  
This sounds actually very likely to happen.

@Dr Outback  
Could be just a placebo. AJ can either keep quiet, which in a way is lying, or tell the truth and make the placebo loses effect.

I didn’t learn anything! :V

@Dr Outback  
But for how long? And for what after-affects?

It has been stated that Granny Smith will feel better after taking the tonic

I just hope that the Flim Flam Bros. doesn’t come in this new episode.