Recently, I had a bit of a thought of a My Little Pony/Disneyland crossover.  Note: The Story would not take place in any part of the My Little Pony: Friendship is Magic Canon.

Twilight Sparkle has been giving a major invitation to Disneyland.  She decides to invite the following to join her.

Spike

Rainbow Dash

Pinkie Pie

Rarity

Applejack

Fluttershy

Discord

Starlight Glimmer

Trixie

Apple BLoom

Sweetie Belle

Scootaloo

Princess Celestia

Princess Luna

Princess Cadance

Shining Armor

Flurry Heart

They all arrived at Disneyland and get to enjoy some time in the entire park.  But deep beneath the park, Chrysalis, Tirek and Cozy Glow would ally themselves with the following villains

Maleficent(Sleeping Beauty)

Cruella DeVille(101 Dalmations)

Captain Hook(Peter Pan)

Ursula(The Little Mermaid)

Jafar and Iago(Aladdin)

Hades(Hercules)

Dr Facilier(The Princess and the Frog)

Zurg(Toy Story series)

Sideshow Bob(The Simpsons)

Thanos(Marvel Cinematic Universe)

General Grievous(Star Wars)

Darth Maul(Star Wars)

To make matters worse, the Dazzlings(Adagio Dazzle, Aria Blaze and Sonata Dusk) join in by causing a little havoc on the theme park with their singing.

Each of the villains(Not just Chrysalis, Tirek, Cozy Glow and the Dazzlings, but also the various Disney Villains) would team up to give our pony heroines a tough time.  Even some villains like Jafar, Ursula, Hades and Maleficent give Discord a run for his money.  

There are scenarios built in that lead to the following

The Cutie Mark Crusaders team up with Bart and Lisa Simpson(With Iago, Cozy Glow and Sideshow Bob giving them a hard time)

Pinkie Pie is kidnapped by Ursula, but gets some help from Ariel

Starlight and Trixie anger the Queen of Hearts and are on the run, much to Chrysalis' amusement

Princess Cadance and Shining Armor show their daughter the whole of Disneyland, only for the bambino to be kidnapped by Dr Facilier and Cruella DeVille

Celestia and Luna meets Elsa and Anna, all while Maleficent gives all four princesses a hard time.

Discord and Fluttershy having the time of their lives.  Hades traumatizes them both

Sunset Shimmer(In human form) meets up with Twilight Sparkle

A team up between Tirek, Thanos and Darth Maul

Rarity, Applejack and Rainbow Dash try to locate their sisters with the remaining villains giving them a hard time.

Bart prank calls Moe the Bartender, who is currently working at the Hearthstone Lounge

Near the end, Twilight is separated from everyone else and is depressed when the villains manage to capture everyone else(Including some of the Disney heroes and those I also mentioned).  It takes some help from Jedi Master Yoda to give Twilight the courage she needs to rescue her friends and some of the Disney heroes from the villains.  It all leads to a final epic battle between the heroes and the villains with the fate of Disneyland on the line.