Ash nazg durbatulûk, ash nazg gimbatul,  
ash nazg thrakatulûk agh burzum-ishi krimpatul.

Three Rings for the Alicorns  
Under the Sky
 
Seven for the Diamond Dogs  
In their halls of stone
 
Nine for mortal Mares  
Doomed to die
 
One for the Dark Dame  
O her dark throne  
In the Land of Equestria  
Where the Shadows lie
 
One Ring to rule them all  
One Ring to find them all  
One Ring to bring them all  
And in the darkness bind them
 
In the Land of Equestria  
The shadows lie.

Magic rings that fit unicorn horns

@Tetragrammapony  
So, Applejack is Sam?

We… are going… to die!

From reddit; mane cast upon obtaining the One Ring:
 
Rarity: Corrupted in a heartbeat. Learns an important lesson.  
Twilight: Tries to study the Ring; is corrupted in two heartbeats. Learns another important lesson.  
Rainbow Dash: Already corrupted, still hasn’t learned her lesson, but she got distracted killing Orcs anyway.  
Fluttershy: Befriends Sauron  
Applejack: Briefly has visions of the magnificent Apple Empire before calling herself an old fool, knowing darn good and well that the biggest garden in the world is nothing compared to a small little thing, honestly tended with care. Doesn’t destroy the Ring, but gets into a fight with Trixie just as Twilight’s corrupted before throwing the Ring (and Trixie) into Mt. Doom.  
Pinkie Pie: Corrupts the One Ring. The Ring fails to learn its important lesson.

Beautiful!

Twilight with the One Ring?
 
Yeah we’re screwed.
 
~STL