Ash vs. The End of the End

I feel the need to speak about how differently the key events of Season 9 would play out in the Order-naries 'verse, but at the same time I don't feel up to making a proper story out of it. I'm going to split the difference with this blog, outlining what would happen without giving too much detail.

First off, Celestia and Luna are not retiring from the throne, but simply planning a year-long sabbatical to give Twilight a chance to get some actual experience running Equestria day-to-day and managing the day/night cycle, since despite being in the official chain of emergency power she's never actually taken charge of the sun and moon.
Because of the events of Order-naries: Storm-chased, the Storm King is not a shattered obsidian statue and thus gets recruited into the Legion of Doom along with Chrysalis, Sombra and Tirek. Instead of Cozy Glow, however, Grogar decides to take a different pony: Ashen Blaze, with the intent of magically reverting him to his old Meis Thamule personality.
Ash, naturally, thinks Grogar is overestimating himself, as Ash is rather immune to magical mental manipulations.
As it turns out, though, Grogar is quite determined to have Meis Thamule. While Sombra is doing his solo act of conquering empires and shattering Trees of Harmony before being destroyed, Grogar submits Ash to such intense magical torture that Ash realizes he's very likely going to die if he doesn't submit. So, trusting that his absence will be noted by the Mane 6 and that he'll be tracked down in relatively short order, he lets Grogar alter his personality. Sadly, it turns out Grogar's lair is well shielded from detection spells.
Thamule comes to two conclusions as Grogar tries to recruit him: while the scruples and morals that Ashen Blaze carefully cultivated have been suppressed, his memories and feelings of camraderie toward the Mane 6 haven't; and that Grogar's magic power, while immense, is vastly overshadowed by a narcissistic ego that can be exploited with carefully chosen words.
So, Thamule outwardly agrees to work with the Legion of Doom, while already plotting to undermine the whole "destroy Twilight Sparkle" plan and, if possible, prep his fellow "villains" for some good old Friendship Lessons.
The mission to retrieve the Banishing Bell goes essentially the same as in canon: Chrysalis and Stormy try doing it solo, then reluctantly team up with everyone and get the bell before agreeing to overthrow Grogar. Along the way, Thamule determines that he doesn't have much of a chance of Friendshipping Chrysalis or Storm King because of their past encounters with him, and he's not likely to get Tirek into a diplomatic mood regarding ponies with the other two around.
It is during the attempt to get into the Canterlot library during the Summer Sun Celebration that things really take a turn. The official story as related later by Discord and confirmed by Ash is... vague at best.
All that is certain is that Thamule crossed paths with Discord in Canterlot, resulting in Discord restoring Ash to his proper personality. Then the two, assisted by all the Element Bearers sans Twilight and plus Spike, managed to capture Tirek and the Storm King and set the festival back on track before any of the Princesses knew anything was wrong. Chrysalis presumably slipped away when she saw things going poorly for her compatriots, as she was never found. Once the pair of villains were presented to the Princesses, and promptly shipped off to Tartarus, Discord volunteered to finish the job by capturing Grogar personally. He popped away and returned a short time later with a stone statue of the dreaded goat, which was put in Discord's old place in the gardens, and the Bewitching Bell, which was sealed away in an undisclosed location.