Background Pony #DC22
Element of Laughter - Makes her older sister cry.
Background Pony #2AE8
Virtues aren’t something you innately possess, they’re something you strive towards.
 
Loyalty makes total sense for Luna, and fits perfectly with her downfall. She poured her heart out for her subjects, and in return she saw only disdain. How can you stay loyal to someone who rejects you?
 
Honesty fits perfectly too. She speaks her mind straightforward and to the point.
 
Laughter… well, other than her evil laugh, she has tried very hard to make her subjects happy. Her inability to do so must have cut her deeply. “Screams of delight is what your princess desires, not screams of terror!”
biojal
The End wasn't The End - Found a new home after the great exodus of 2012

Right Twice a Day
To be honest, luna having the element of loyalty was always my headcanon.
Vivacious Sun

Pity the likelihood of an episode that actually covers Discord -> NMM schism in any form of detail is so unlikely.
 
In the end all we have are factions trying to defend two very vague characters that only serve as ‘woobie questgiver’ (Celestia) and ‘important event prop’ (Luna)
d715
The End wasn't The End - Found a new home after the great exodus of 2012

@Align  
Yeah but when is Luna every funny? She’s dead serious all the time. The only time she’s remotely goofy is around kids
 
Anyway I think we can agree the two need to switch generosity and Laughter
Align
Wallet After Summer Sale -

Elements don’t seem to be assigned to whoever has the most of whatever personality trait, but rather someone who struggles with and especially highly values it.  
AJ lies time and again, RD is torn between friends and dreams, Twilight was a loner most of her life, etc.  
Otherwise Pinkie Pie would be the element of friendship.
Mad Black
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The End wasn't The End - Found a new home after the great exodus of 2012

So Celestia is magic, kindness and generosity and Luna is Loyalty, Honesty and Laughter.
 
Luna’s 3 don’t mix to well, considering how she was in the beginning of the nightmare night episode.
Soufriere

Sunset Shimmer Fan
I… don’t think the animators really thought out which Princess was supposed to have which Elements of Harmony.
 
According to this, Luna has Loyalty, Honesty, and Laughter. That last one definitely doesn’t apply to her, and Loyalty is pretty sketchy too. Honesty, though, yeah that one’s Luna’s. Celestia has Kindness, Generosity, and Magic. Sure those all fit, but I think Luna deserves to have Generosity more than Sunbutt did.
 
CONCLUSION: Back then, both Princesses could each bear all six elements by themselves. FURTHER HEADCANON: Luna forsook the Elements; Celestia was forsaken by the Elements after banishing Luna (this is pretty much canon based on what Celestia said in Ep.27).
Mojo

I like Luna with Loyalty, it makes her downfall even more tragic.
bico-kun
An Artist Who Rocks - 100+ images under their artist tag
Artist -

I always liked the idea that the princesses lost their connection with the Elements due to various events which reversed their behavior and rendered the gems inert. Kinda why I was hoping Celestia would have honesty, since she tends to be a trickster mentor.
supermanhulkjesus

I don’t think there’s any significance to which elements they’re holding. When the main six used them, they were assigned their elements and they only worked as long as there was friendship and harmony between them. The rules were apparently different for Celestia and Luna.
Mayojar77
The End wasn't The End - Found a new home after the great exodus of 2012

@Trickquestion  
Loyalty to yourself is still loyalty.
supermanhulkjesus

@sargesprinkles  
With her mouth hanging open and her pupils dilated the way they were, she looked as if she was drugged to me.
Mister Friendly

Princess Celestia has the Element of Generosity  
Gives Luna 1000 years on the moon  
Your welcome!
d715
The End wasn't The End - Found a new home after the great exodus of 2012

@HJSDGCE  
Which is double irony as her normal self takes things very serious
 
ie not very funny
Trickquestion
The End wasn't The End - Found a new home after the great exodus of 2012

Well, Loyalty also locked on to Rainbow Dash. I guess that one’s just defective.
Background Pony #94E7
Observation: Characters often reverse personality traits when confronted by situations that conflict with their self-definition (Cutie Mark Failure Insanity Syndrome).
 
Luna, in response to the perceived lack of devotion towards her night, may have reversed the devotion she felt towards her subjects.
Lord WyrmSpawN
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Lingering Wyvern
Honesty:we’ve yet to hear her transmit false information or withhold useful tips.
Background Pony #514A
@HJSDGCE  
Loyalty to her night sky, how dare they not give it the respect it deserves.
sargesprinkles
The End wasn't The End - Found a new home after the great exodus of 2012

@Garth01  
i personally think it’s more of a “well this is new” reaction  
but that’s just me
Garth01

@sargesprinkles  
It’s kinda up in the air right now. in the Animatic she has a look of fear. In the final version she looks like she is in pain just before going into some kind of trance.
Garth01

Kinda irrelevant considering unlike the Mane6 the Elements did not appear to the Princesses they just took them from the Tree.
Mayojar77
The End wasn't The End - Found a new home after the great exodus of 2012

@HJSDGCE  
You can only be loyal to those that are loyal to you.
Ripple_Shine
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It can suck when your loyalty goes unrequited. That’s all the more I’ll say.
Scrabbleman
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[screams in German]
@Crowley  
I agree with Luna having laughter.  
Her evil laughter is really great.
 
And at least she was honest to her sister about making eternal night.
 
Loyalty… Fuck.