Well, a little story here to clear the set up:
 
Rarity was the Mi Amore Cadenza’s fight club (royal kinky club for a nobility where mares from all the Equestria fights for glory, bits or solve disputes by dueling in the ring) foxy boxing champion. Suri Polomare challenged her once, but it ended in crushing defeat for her and moreover Coco Pommel happily flitted away to Rarity.  
She would seek revenge every day until she had the nerve to write a letter to Rarity for a REMATCH. No rules, no mercy, just these two lovely mares… This time Suri Polomare uses Zecora’s amazon potion to surprise her rival. But it works only along with regular ordinary hard workouts (and no longer than for six months), so nonetheless the fashion mare trained thoroughly and methodically.  
How the lovely mare can hide so changed body? Of course rumors quickly reached the Carousel boutique and Rarity visited Zecora, started her workouts too.  
Sadly for the champion Rarity she was KOed and humiliated in front of all the audience along with all the four Princesses.  
After the fashionista recovered the first thing she did was the call to Suri to set up the REMATCH. Vicious Suri as a champ insisted on tag-team match, to force Coco fights against the team of the object of her affection… Both rival pulls their closest mares into this - Suri’s bdsm slave Coco and Rarity’s lover Fluttershy. Zecora is more than happy to sell more amazon potions!  
Four month later from the last amazing bout, two teams meet each other in the Mi Amore Cadenza’s fight club…
 
 
Big thanks to isisazza for help at this (and more)