War for existence

On the other side of the portal, the mane 6 fell out inside of a castle throne room. When they got up, they noticed several human-like beings with mushroom heads and a princess in a pink dress staring at them.

"Oh, my" said the Princess. "Who are you"

Twilight replied "My name is Twilight sparkle, your majesty. This is Applejack, Rainbow dash, Fluttershy, Rarity, and Fluttershy. We came from our home world of Equestria seeking help. Just today in our world, thousands of strange metal ships came out of a portal and started destroying everything in sight."

Suddenly, a very loud roar was heard. "Princess Peach!!!" yelled the voice. A huge fire breathing lizard with a spiky shell dropped from a hole in the roof.

"Bowser, this is not a good time, though every time is not a good time. But this is more not a good time than ever." said Princess Peach. Seconds later, two brothers with mustaches, one wearing red with blue overalls and the other wearing green with blue overalls, ran in.

"Bowser" said the taller one, "You're not going to get the princess this time."

The two brothers were just about to fight Bowser when the rumbling and the flash that signaled a portal opening happened. A few ships came out and landed right next to the castle, releasing several robotic creatures. "Attention" said one of the creatures, "We have tracked 2 Unicorns, 2 Pegasi, and 2 Earth ponies to this universe. Send them out and we will spare your universe, for now. Refuse, and we will make you watch as we destroy everything you have ever known before we kill you."

Peach, Bowser, and the two brothers argued over whether they should give the ponies over

"I say we give those creatures the ponies." said Bowser.

The shorter of the two brothers replied, "But Bowser, they said that they would destroy our universe whether we hand them over or not."

"Now, you go and pack what you'd need from your homes. I hate to leave my kingdom, but it'll be destroyed either way. I say we go with these ponies and stop this threat to both of our universes." said Princess Peach.

"Fine" said Bowser

"I'll send word to the Prince Peasley, Prince Dreambert, the Yoshi clan, and Rosalina to follow us."

"And I'll send word to the Shroobs, Cackletta, Fawful, and Midbus, and Antasma. If this threat is as big as these ponies say it is, then we'll need all the help we can get. Even from our enemies." said Bowser

30 minutes later, everyone was there. "Listen" said Princess Peach "I know that some of you don't want to see each other, but we have brought you here for a reason. Twilight, tell them."

My name is Twilight sparkle, and all of existence is in danger. There's a new villain named Lord Doom, he came to our world and threatened to burn every universe there is, ours included. You may not like each other, but either you sit here fighting until you and everything you know is gone, or you join us to help us in the war for existence."

At this, the rest of the heroes and villains of that universe arrived. It was time to move onto the next universe.