A Corridor of Darkness opened up within a hidden cavern just below the Castle of the Two Sisters, the person stepping out of it was none other than the Keyblade Master of Darkness, Xehanort.

"Hmm...what have we here?" he asked no one in particular as he gazed at the crystalline tree, which was slowly losing its glow, "This is without a doubt the artifact that prevented my arrival..." he opened his right palm and hovered it in front of the tree, "let us fix that, shall we?"

Darkness flowed from his fingertips into the tree, causing its glow to die out instantly. Just then, black, thorny vines sprouted from the ground, snaring the tree and strangling it. They went after Xehanort as well, but with a wave of his hand, he countered with a vast aura of darkness, making the vines back away, fearful of his power.

"Hmph. I don't recall coming here to become plant fertilizer." he stated as he exited the cave and entered a ravine. He turned around and looked up at the Castle of the Two Sisters, decrepit and in near ruins. He sneered, "Oh...I do believe I am getting some where now."

Final Mix Chapter: Research

After wandering around the ruined castle for some time, Xehanort finally found the once royal library, but like the rest of the castle, it was in near ruins; parts of the ceiling were crumbled onto the floor, book littered in large piles, and the vines from before growing all throughout the castle goes without saying. Xehanort began searching the shelves for anything of interest, but found nothing. Just before he gave up, he came across a tome labeled, "Dangerous Threats To Equestria", and with a sneer, he plucked it off the shelf and began researching.

"Hmm...'Discord'...'King Sombra'...'Tirek'...'Changelings'...'Nightmare Moon'..." he read off the names he found, the latter's backstory reminding him of Riku when he gave in to darkness and a certain feckless youth who became his new vessel, then he saw a subject within that piqued his curiosity, "...'Tartarus; a prison for the worst criminals in Equestrian history'..." he sneered once again, and his eyes then laid upon an open book with blank pages inside it, "Hmm...perhaps I should chronicle my findings..." he looked back at the tome in his hand, "I suppose even a utopian world like this has its dark corners..." he chuckled darkly at thought of having multiple candidates for his Seekers of Darkness.

Final Mix Chapter: Xehanort's Journal

With quill in hand, he began jotting down information from a new book he found about the Elements of Harmony after finishing his research on the dark entities that reside in Equestria.

"...'The Elements possess a powerful magic that can seal away dark entities...example #1: Discord was turned into a stone statue after Princesses Celestia and Luna used the Elements on him...example #2: After Luna's descent into darkness and becoming Nightmare Moon, Princess Celestia used the Elements to seal Nightmare away in the moon, giving her the nickname, The Mare in the Moon'...Interesting."

After Xehanort feels he has collected enough info, he took his newly-found journal and begins to leave, only to find a secret room that contains another journal on a pedestal. With a few curls of his fingers, his darkness conjures another pedestal and places his upon it, closing the secret room back up afterwards.

"Should Sora or any of his friends find this, it should give them a few clues as to what my next move will be...if I am betting on luck to help me, they may get the wrong idea and chase after a wild goose, as the saying goes."

Xehanort began to take his leave from the decrepit castle and proceed with the next part of his plan.

Author's Notes:

EDIT: Had to change some of this chapter because of an error pinkiepierocks pointed out, thanks buddy

Final Mix Chapter: The Stage is Set

After Xehanort witnessed the vines disappearing in several rainbow lights, he sneered as he felt everything has gone according to plan; Sora came to Equestria and saved the day, just as he always did for every other world.

"And now, the stage is set...all I need to do at this point...is simply retrieve my 13th Darkness."

Xehanort walked down the stairs back into the ravine and made his way to the cavern with its current inhabitants unaware of what's coming before them...

Author's Notes:

And that's the last one! I hope you guys liked it!