My Little Pony: Friendship Is Magic is a surprisingly creepy show that has some dark moments, hiding behind all the tame, happy, and heartwarming moments.
There are a large number of monsters/villains. Nightmare Moon, Discord, Queen Chrysalis, King Sombra, Sunset Shimmer, the Chimera, Tirek, and the Dazzlings are some of the more intense ones.
Some characters have mental or emotional breakdowns; they are never violent, just intense. Most are generally uncomfortable due to coming out of nowhere.
In "The Stare Master", Twilight Sparkle and a chicken are turned into stone after an encounter with a creature called a cockatrice (half chicken half snake).
The first two episodes of the second season, "The Return of Harmony", are very bizarre: a chaos-loving villain, named Discord, is a strange and eerie creature called a "Draconequus" (the head of a pony and a body of all sorts of other things; in Discord's case, he has the right arm of a lion, the left claw of an eagle, the right leg of a lizard, and the left leg of a goat. Additionally, he has a bat's right wing, a Pegasus' left wing, a horse's mane, and a dragon-like snake's tail with a white tail tuft). Discord is also very evil, as he told one of the ponies that if the pony goes to save her own friends, her hometown would get destroyed, and the ponies living there will be killed, so she has to save her hometown and leave her friends. Later episodes' flashbacks would reveal that, prior to the reign of Princesses Celestia and Luna, Discord ruled all of Equestria, causing trouble wherever he saw fit.
In "Lesson Zero" (which has become a popular Internet meme due to this), we see the main character, Twilight Sparkle, lose her mind throughout the second half of the episode, which could be quite disturbing and unnerving for younger viewers.
In "Baby Cakes", a baby pony is seen walking upside-down on the ceiling, giggling demonically. It's a quite creepy scene, and also a reference to the 1996 film Trainspotting.
There are many emotional scenes that are rather intense in terms of sadness-level for a kids show. They are all animated perfectly to fit the situation, making us feel compassion for the ones who suffer, and the acting is spot-on too. One scene is in the episode "Putting Your Hoof Down" where Fluttershy has become very mean, but tries to be assertive; this puts her in a position that makes her shout at anypony. She starts to bully Pinkie Pie and Rarity. This makes them both cry.
In the two-part second season finale, "A Canterlot Wedding", where Twilight's brother Shining Armor is about to marry Princess Cadance, Twilight notices Cadance acting mean to her friends. When Cadance discovers Twilight's on to her she casts a ring of green fire around Twilight causing her to disappear and ending the episode on a disturbing cliffhanger. The following episode picks up directly where the last one left off with Twilight waking up in her new location under Canterlot Castle, Cadance appears as an illusion on all the crystals in the cavern making supervillain-like threats while Twilight destroys the crystals in panic and frustration, resulting in her finding the real Cadance, who is also trapped in the caverns. Later in the episode, Cadance and Twilight stop Shining Armor from marrying the impostor Cadance, who reveals herself to be Queen Chrysalis, the ruler of the changelings. Her appearance may be frightening to younger viewers, as she has insect like wings and back, holes in the bottom of her legs, and large green demonic eyes.
In the third season premiere, "The Crystal Empire", the villain is a demonic being called: King Sombra. He is the embodiment of evil, and he also has a mirror that shows the worst nightmares a pony can see. Sombra doesn't speak much, he growls and snares all the time, saying that he is much more a looming threat. A true demon.
In the third season finale, "Magical Mystery Cure[/i"], Twilight appears to have been obliterated by a powerful energy; however, she has merely been transported to a limbo where Celestia rewards her with a pair of wings and the title of Princess Twilight and then returns her safely home.
In "[i]Castle Mane-ia", the cast spend most of the night in a derelict castle the environment is very spooky with the characters becoming increasingly frightened, there is also a shadowy figure playing an organ which results in various booby traps triggering, although this only turns out to be Pinkie Pie.
In the same episode, Fluttershy is lead to believe her pet rabbit is crushed to death under a pillar.
In "Bats!", Fluttershy is turned into a vampire (which feeds on apples, not ponies) and her appearance changes, her fur becomes pale, her mane and tail turn frizzy, her eyes turn red, her wings turn into bat wings and her teeth turn into fangs. Her new mentality causes her to shun her friends. She is returned to normal be the end of the episode, but a closeup of her mouth reveals that she still has a fang, implying that she could become a vampire again.
The villain of the fourth season finale, "Twilight's Kingdom", Tirek, is a diabolical villain and he resembles a demon-goat. He is very powerful and intense, and has the power to drain other ponies magic. He is the most dangerous and difficult opponent that the Mane 6 have ever encountered. He is also a rather disturbing character for a kids show.
In the two-part season five premier, the mane six travel to a town full of "assimilated" ponies, they all have dull coloured fur, identical hair styles, very creepy forced smiles and their cutie marks removed and replaced with an "equals" symbol, they often crowd around the mane six which is very creepy to see and the villain of the episodes Starlight Glimmer almost succeeds in assimilating the mane six, Tirek aside this is the most powerless the main characters have been.
In the episode "Tanks for the memories" the episode revolves around Rainbow Dash trying to prevent winter from coming so that her beloved pet tortoise Tank doesn't go into hibernation. By the episode's end, it dawns on Rainbow Dash that she can't prevent the hibernation and she breaks down crying, which shocked many people as Rainbow rarely shows her emotions. The episode becomes much sadder when you realise it's a metaphor for the five stages of grief
In the two part finale to season 5, Starlight Glimmer returned to challenge Twilight Sparkle, using a time traveling spell, she travels back to the time where Rainbow Dash performs her first Sonic Rainboom and prevents this from happening so that Twilight and her friends never get their cutie marks and never meet, however, the resulting butterfly effect results in King Sombra never being overthrown and him with the Crystal Empire are now at war with Equestra, the battle are violent and intense (for MLP) and Rainbow Dash is seen with a prosthetic wing, how she lost her own wing is unknown. Twilight keeps going back to stop Starlight but keeps failing, each new butterfly effect being worse than the last, including Queen Chrysalis and her changelings taking over Equestra with only a small resistance left, Nightmare Moon taking over, Tirek destroying everything, Duscord ruling the world until finally Twilight shows Starlight the butterfly effect with only a barren wasteland and no life remaining. These can all be very shocking.
19/50 - Despite some darker moments, overall, it is a very light and happy show that attempts to teach children to be nice and accepting of others, although, the series is many times more darker than the previous versions of My Little Pony, which is actually for the best.
Recommended for children around 8+ due to its quite bizarre, dark, and sad nature. Probably the darkest children cartoon in a long time (don't let the DVD covers and promotional material fool you!)