Opalescence

Opalescence, or Opal for short, is Rarity's pet cat. She is introduced in the episode Suited For Success.

Development and design
According to Lauren Faust, "Opal Essence was originally [named] Ruby", "and about 5 other names in between", according to Andrea Libman. The name was changed because most of those gemstone names were legally trademarked for toys.

Opalescence looks like a typical Persian cat, with white fluffy fur, a wide face, and shortened muzzle. She wears an opal-studded collar around her neck, and a purple ribbon on the top of her head. Opal's scenes are sometimes accompanied by harpsicord music, for example when she luxuriously curls up on a roll of cloth in Suited For Success.

Personality
She is irritable and often yowls and hisses at her owner Rarity and other ponies, but not at Fluttershy. She is pleasant enough in the park with Rarity on their pony-pet-playdate in May the Best Pet Win!. Opal exhibits a sort of fashion sense; in Suited For Success, she happily rubs herself against the dresses that Rarity designs for Rarity's friends, but shows disgust at the dresses that the friends custom-order. In Sweet and Elite, Opal reminds Rarity of Twilight Sparkle's incomplete dress by impatiently tapping on Rarity's design sketchpad.

Season one
Opalescence first appears in the beginning of Suited For Success. Rarity thanks Opal for her assistance and asks for her advice, while Opal seems bothered and annoyed by being given things to carry and being carelessly flung off the fabric that she was sitting on. Rarity confides in Opal throughout the episode, but Opal only hisses and meows in return. When Rarity locks herself in her room after her failed fashion show, Rainbow Dash strands Opal in a tree to lure Rarity out of the room; Opal shakily hugs a branch while meowing in fear.

In Stare Master, she swipes and chops off a lock of Sweetie Belle's mane and offers a smug look after Sweetie Belle suggests that her special talent might be caring for animals. In Owl's Well That Ends Well. Spike takes Opal's toy mouse, which he uses as a ketchup-bloodied carcass to frame Owlowiscious for its murder.

In The Best Night Ever, Twilight Sparkle uses magic to turn Fluttershy's mice into stage horses so that they can travel to the Grand Galloping Gala. Opal thwarts their plan by pouncing on the mice-like horses, who gallop away.

Season two
In May the Best Pet Win!, Rainbow Dash puts her prospective pets through a series of tests, one of which is a test for "guts". The applicants quake in fear when Rainbow Dash challenges them to take away Opal's favorite toy, a stuffed mouse. One of the contestants, a butterfly, successfully mesmerizes Opal and whisks away her toy. Tank, the tortoise, tries to trap Opal in her carrying case by flipping it over her, but she gets out of the way in time and fiercely scratches at his shell. Near the end of the episode, Tank does succeed in taking away the toy from Opal while she is busy scratching his shell.

Opal accompanies Rarity to Canterlot during her stay at Canterlot Castle in Sweet and Elite. Opal indulges in many of the royal city's splendors with Rarity, and when Rarity decides to create a new dress as a gift for Twilight's birthday party, Opal tries to keep her focused on her work. When Twilight Sparkle and the rest of the friends unexpectedly show up at Canterlot to host the party there, Rarity lies, claiming that she had to stay to take care of a "sick" Opal. Rarity hastily soaks an irate Opal in water to feign illness. Fluttershy gives the "poor baby" her usual tender love and care, hoping to make her "better".

Season three
In Too Many Pinkie Pies, Opal appears among the ponies and animals hiding in the woodland critters' tree home.

In Just for Sidekicks, Spike volunteers to petsit for her in exchange for a jewel (albeit a very minuscule one). Opal is shown to have many specifications for comfort, including needing to be kept at a constant 81.4 degrees of temperature. She is shown in this episode to now have something of a bond with Tank, as they nuzzle briefly upon seeing each other and Tank carries her through the air at different times. Opal also helps Tank to hide on the train when Spike, the Cutie Mark Crusaders and the other pets are trying to avoid detection by Rarity and her friends.

In Magical Mystery Cure, Opal appears in Fluttershy and Rarity's flashbacks.

Season four
In season four, Opalescence appears in Princess Twilight Sparkle - Part 1 as the plunderseeds that attack Ponyville mess with Rarity's magic that causes Opal to fly around the room. On Maud Pie, Opal attends the pony-pet playdate when the Mane Six meet Pinkie Pie's sister Maud for the first time. In For Whom the Sweetie Belle Toils, Opal and Rarity evesdrop on Sweetie Belle screaming in anger in her bedroom, and in Testing Testing 1, 2, 3, Opal portrays as Princess Luna on Fluttershy's play.

Season five
In season five, Opal appears in Do Princesses Dream of Magic Sheep? as Rarity grooms her at her boutique. Rarity, having not had enough sleep, accidentally pokes Opal's lower back with her comb. Opal also appears in Canterlot Boutique playing with her toy mouse. She gets offended when Rarity mistakes her for the mail pony.

Season six
In Flutter Brutter, Fluttershy employs Zephyr Breeze as Rarity's assistant and asks him to dye all of the fabrics. However, after seeing Opal play with the paint, he gets her to do all of it.

IDW comics
Opalescence appears on page 3 of. A bowl can be seen with the letters "Opalescens".

The Elements of Harmony guidebook
''OPALESCENCE, or Opal for short, may seem fluffy and sweet, but that's only when she's manipulating her owner, Rarity. This feisty little kitty has been known to hiss when she doesn't get her way!''