Title: Crisis of Infinite Harmony.

Main Characters: The Main Six, Spike along with several other characters.

Genre: Crossover, Alternate Universe, Comedy, Dark, & Adventure.

Cannon Placement:
Hasbroverse: After Chapter 2.
Lunaverse: After Crisis on Two Equestrias.
Manehattanverse: After The Wrong Place at the Right Time.
Cadanceverse: After The Music of Ponyville.
Flipverse: After Boast Backers.
Dashverse: After Hot Heads, Cold Hearts and Nerves of Steel.
Shimmerverse: After A Different Sunset.
Crisisverse: Right before the start of the story.

Premise:
The story starts when right after Megan and Twilight Sparkle arrive in Equestria. As it turns out, another portal has opened in another part of the Everfree Forest. Not taking any chances the Mane bring the Element's of Harmony to close the portal. Sadly, the clashing energies causes a backlash of energy that make the portal stronger and threatens to suck them all in! However, a strange entity pushes them back, while the beams from the Element's are sucked in before the portal implodes on itself, causing a massive explosion…

...when the Mane awaken, they find themselves back in Ponyville. Where Megan reveals that after the explosion, the Element's have vanished, many strange occurrences involving dimensional rift's have been happening around Ponyville, Canterlot, Manehattan, and many other cities across Equestria! Not only that, but there have been reports of ponies seeing doubles of each other, but their "other selves" are acting weird;

Why does Rainbow Dash think Celestia is her teacher?

Why does Daring Do think she's the Element of Honesty?

Who is this strange Dragon and why does she look like Twilight?

Who is this “Fiddlesticks” and why does she think she’s the Element of Laughter?
Why is Fluttershy calling herself Element of Generosity?

As more and more question's start popping up, help comes in the form of a Chronomancer named Tick Tock, and Trixie...the Element of Magic?! The two reveal that their attempt to close the portal resulted in several other Element's being flung out of their own world and into their own, and unless they get them back to their own world, their dimensions will collapse on each other! With no time to waste, the Mane Six with their new allies embark on a journey to find the other Element wielders! But unknown to them, another group of Mares have arrived in Equestira...and their anything but friendly...

Who are these Six new mares? Can the Mane Six stand against them? And who opened the rifts in the first place...?

3659968

So basically sort of similar to the Crossover-verse and Multiversal Harmony?

3659984
Yes but with a lot more characters.

3659985 While a mega-crossover is enticing, this idea, I fear, lacks an certain Je ne sais quoi. Perhaps create a villain wholesale instead of using ones from another fic? Perhaps include canon characters(Elements & Saviors are close enough, if you don't wish to include anything beyond the first 25 episodes)? Or maybe create a new incident rather than piggyback off one from another canon? Here's hoping this helps and I'm not just annoying you!