Inanimate objects

Throughout the series, many characters aren't even living characters at all. Inanimate objects are sometimes used in shows to add to the humor and insanity of the episodes.

Bloomberg
Bloomberg is the name of an apple tree that Applejack and her friends take to Appleloosa in Over a Barrel.

The episode opens with Applejack placing the tree in its own coach while cooing at it affectionately. The gag elaborates as she places it in its own bed, talking to it as if to a baby, and reading bedtime stories to it. Along the way, a buffalo tribe manages to release its coach from the rest of the train, meaning to keep it from being planted in Appleloosa, because the apple orchard is taking up space for their stampeding. In the end, they find an agreement and Bloomberg is happily planted on top of a hill.

Pinkie Pie's imaginary friends
During the episode Party of One, Pinkie Pie comes to the conclusion that Twilight Sparkle, Applejack, Rarity, Fluttershy, and Rainbow Dash are avoiding her latest party, believing they no longer want to be her friends. She soon replaces them with inanimate objects. These "new friends" are:
 * Mr. Turnip: a bucket of turnips, slight slow speaking.
 * Rocky: a pile of rocks with a Bronx accent.
 * Sir Lints-a-lot: a clump of lint, speaks in a slightly sophisticated accent.
 * Madame LeFlour: a sack of flour who speaks with a French accent.

While Pinkie puppeteers and voices the objects, from her own point of view the objects are moving and speaking on their own. They denigrate Pinkie's friends, persuade her to leave her old friends, and praise her when she agrees. The party ends when Pinkie is dragged by Rainbow Dash to the Sweet Apple Acres barnhouse, where she attends a party celebrating her birthday, secretly organized by her friends.

Tom
Tom is the name Rarity gives a large rock in The Return of Harmony Part 2, thinking that it's a diamond.

Rarity, while under the influence of Discord in The Return of Harmony Part 1, digs through a slab of rock which has three gems reminiscent of her cutie mark embedded in it. She breaks apart the rock and extracts a large diamond, acting fawning and protective towards it. When Twilight Sparkle arrives, the "diamond" appears as a simple boulder, making it clear that only Rarity sees it as a diamond. Rarity refuses to part with it for the majority of both episodes, and Twilight even helps Rarity carry it in hopes of eliciting a positive response from her.

The next episode, Twilight asks her friends into her library, but Rarity remains outside and says she's on to Twilight's plan to steal "Tom" from her, addressing the boulder by name. Resigned, Twilight carries the boulder inside for Rarity and crashes it through the door, leaving a giant hole in the wall. Later, as the other ponies venture back outside, Rarity delays in order to push "Tom" ahead of her. Twilight magically levitates the rock, then the scene cuts to outside the library, and Twilight is heard exclaiming "Look out, here comes Tom!" before the boulder flies out the window, leaving another giant hole in the wall.

Near the end of the episode Twilight reverts Rarity to her normal self, and the illusion that the boulder is a diamond goes away. She rolls it out of her house and asks her friends to never speak of it again.

Smarty Pants
Smarty Pants is Twilight Sparkle's old doll from when she was the Cutie Mark Crusaders' age, which is introduced in the episode Lesson Zero. According to Twilight, Smarty Pants comes with a notebook and quill.

When unable to find and solve a "friendship problem" to relate to Princess Celestia, Twilight exclaims that she is going to create one herself. She takes Smarty Pants out of a blue and gold chest in the library and presents it to the Cutie Mark Crusaders, trying to provoke an argument between the fillies that she can solve by emphasizing the importance of sharing.

However, her plan goes awry when the Crusaders turn out to be unenthusiastic about the ragged old doll, going so far as to attack each other over who should play with it first. Twilight enchants the doll with a "want it, need it" spell, which makes the Cutie Mark Crusaders fight over who gets to play with it, much to Twilight's delight. However, she doesn't manage to break up their fight, and asks Big Macintosh, who was passing by, for assistance. He retrieves the doll, but falls under the spell and takes it for himself, eventually causing a mob of Ponyville's citizens to desire and fight over the doll.

The doll is abandoned by most of the ponies when Princess Celestia intervenes and lifts the spell, but Big Macintosh, showing a genuine want for the doll, runs off with it. It is unknown if Big Macintosh is still in possession of the doll as it hasn't been shown since.