Well, now that things have taken a fairly dark turn for Derpy, let's see just where it can go next...

"Shadow Hooves?" Twilight asked.

"Yes!" Shadow Hooves answered in both her and Sombra's voices simultaneously. "Derpy Hooves was weak, clumsy, and foolish, so I have rightfully replaced her! I have been blessed with the awesome powers of King Sombra, rightful ruler of the Crystal Empire! It is through them that I shall achieve ultimate justice! I shall right the wrong, punish anypony who was ever irate towards me!"

"Jeez, Derpy..." Rainbow Dash said. "...you really know how to let anger get to you, huh!?"

"Because it gives me power! Anger, hate, and rage... all of those emotions fuel your desire for vengeance, which serves as a driving factor for power!" Shadow Hooves said.

"Okay, uh... Derpy..." Pinkie said. "...you really are a few teaspoons of baking powder short of a muffin."

"SILENCE!" Shadow Hooves thundered. "Now... time to have a little fun with the ones who put their faith into something as stupid and pointless as friendship!"

With that, Sombra's horn started to glow a malevolent yellow on top of Shadow Hooves' head, and shot a bolt of magic straight at Fluttershy. It hit her, but she simply flinched; it did not appear to do anything to her.

"Fluttershy!" Twilight said. "Are you okay?"

Fluttershy closed her eyes and hung her head down. "Ohh... I feel weird..." she said, placing a hoof on her belly.

Twilight glared at Shadow Hooves. "What did you do to her, Derpy!?" she demanded.

Shadow Hooves smirked. "Little birdie told me that Fluttershy... would like to be a tree."

"What...?" Twilight uttered as her eyes went wide.

"Um... excuse me..." Fluttershy said, quietly.

The rest of the ponies looked back at Fluttershy, who was now standing on her hind legs, which appeared to be merging with the ground. Her hooves were turning into roots! And her skin started looking rugged as it became tree bark.

"EEK! G-girls... help...!" Fluttershy shrieked, trying to free her hind legs. "...I-I can't move...!"

Shadow Hooves laughed. "No matter. Once this is all over, all you will need to do is photosynthesize carbon-dioxide and water for your sustenance! Ha ha ha!" she said.

Fluttershy started growing in height quite rapidly as her front legs were forced upwards at an angle as pink leaves started to sprout from them. Her mane stood out more as it became the same leaves. Her hind legs merged together to form a singular trunk. Soon, Fluttershy's change stopped, leaving her as a large oak-ish tree, with a light yellow trunk and pink leaves, with her Cutie Mark at the base of the trunk. Her face was the only thing unchanged, but it was now made of yellow bark and a little above the two peripheral branches that had once been her forelegs.

"Oh, dear..." Fluttershy said, upon examining herself as best as she could.

"Well, ah'll be!" Applejack said angrily. "That there is some o' the most fouled-up manure ah've ever laid eyes on!"

"You don't turn ponies into trees!" Pinkie said. "That's just mean!"

Shadow Hooves chuckled. "And just what precisely do you plan to do about it?" she asked.

"Well, darling..." Rarity began. "...you will turn yourself in to Princess Celestia immediately! If not, you shall suffer even greater consequences!"

"Oh, I don't think so..." Shadow Hooves said, firing a magical bolt at Rarity. "...you marshmallow!"

In less than a heartbeat, Rarity's entire form was sucked into a single spot the size of a small barrel. Rarity's face was on it, as were her mane on top and tail on the back... but she had become a very soft-looking mass with her Cutie Mark on the side. Shadow Hooves had turned Rarity into a marshmallow.

"Oh my...!" Rarity said, looking at herself. "What have you done!?"

"HA HA HA HA!" Shadow Hooves laughed. "Learn to face the truth, darling. You are a marshmallow, which you always have been, figuratively speaking."

"NO!" Rarity said, just before bursting into tears. "I am NOT a marshmallow!"

"Ooh!" Pinkie said, hopping over to Rarity. "You look tasty!"

"P-Pinkie Pie..." Rarity began, still crying a bit. "...if you dare e-eat me... I will not hesit-tate to give you a most d-d-dreadful stomachache..."

"Oh, curious about all this, are we...?" Shadow Hooves said. "Well, why don't we give your Cutie Mark a more symbolic meaning, then?"

Shadow Hooves shot a bolt of magic at Pinkie. Once the flash went out, Pinkie found that one of her hind legs was tied to a stake in the ground that Shadow Hooves conjured.

"Um..." Pinkie began. "...what does this have to do with my Cutie Mark?"

"Heh heh... just you wait for the spell to take effect." Shadow Hooves said.

Immediately after Shadow Hooves finished speaking, Pinkie's stomach started groaning and gurgling.

Pinkie placed a hoof on her front. "Huh? My tummy feels funny..." She said.

A few moments later, Pinkie's abdomen started to distend. It became so large that it pressed the ground, lifting her off her feet. Eventually, the pressure moved into her back, making it bulge outward as well, and into her limbs, making them thicker, and causing her cheeks to puff up.

As Pinkie continued to inflate, she began to rise off the ground. She would have drifted off, had it not been for the rope tethered to her leg.

"Woah...!" Pinkie said, her voice slightly muffled as her head was being sucked into her expanding body. "Now I know how a party balloon feels!"

Eventually, the gurgling sounds from Pinkie's stomach stopped along with her inflation. She was left hovering in the single spot, her body perfectly round.

"Grr..." Twilight growled. "...think about what you're doing, Derpy!"

"I am very much thinking about it..." Shadow Hooves said. "...and I think it's quite fun!"

"Wheeeeee!" Pinkie said, spinning herself around. "She's right! This is fun!"

"Hmph..." Shadow Hooves nodded. "...at least some here can understand my humor."

"That's it! Ya've gone too far this time, Derpy!" Applejack said.

"Oh, you believe that you can stop me?" Shadow Hooves said.

"Oh, ya'll bet yur darn tootin' we can!" Applejack said.

"You know..." Shadow Hooves began. "...part of your name happens to be masculine. To be precise, the "jack" portion."

"Whaddya sayin'?" Applejack asked. "Ya'll makin' fun o' me?"

"Oh... in a manner of speaking." Shadow Hooves said. "So, let's make your name a little more... proper, shall we?"

Shadow Hooves fired a magical bolt at Applejack... and she became a stallion.

"Oh mah stars!" stallion Applejack said in a male voice. "Ah thought Trixie would've been the last one ta do it!"

"And now, I might as well get you, Rainbow Dash." Shadow Hooves said. "Wouldn't want to leave you out of the fun!"

Shadow Hooves shot a bolt at Rainbow Dash, who attempted to fly away, but failed. She was hit, and all of a sudden, her colors began to randomly scroll through the entire rainbow spectrum, and her eyes were brightly-lit, doing the same thing.

"W-woah...!" Rainbow Dash said. "I-I'm seein'... weird stuff! Really weird stuff!"

At that moment, a light teal energy bolt zipped past Shadow Hooves' face. She looked to see that it was Starlight who shot the bolt.

"Oh, a challenger we have, hm?" Shadow Hooves said.

Starlight glared. "Derpy, it's time for you to stop! This is not who you are! Submit yourself to the powers of Harmony, and we'll get you back to the way you were!" she said.

"Oh, you're hilarious!" Shadow Hooves said. "But I'm afraid you will never get Derpy back!"

"Oh, you bet we can!" Twilight said as she stood at Starlight's side. "We did it with Nightmare Moon, and we can do it with you!"

"Come now..." Shadow Hooves said. "...what's the harm in some benign transfiguration spells?"

"I DON'T WANT TO BE A MARSHMALLOW!" Rarity bellowed.

"Drama Queen!" Shadow Hooves mocked.

"Um... excuse me, but..." Fluttershy began. "...I really don't want to be a tree now, and I would like to be turned back into a pony... I-I mean, if you want to, that is..."

"And ah ain't gonna steal the spotlight from Big Mac as Apple Bloom's favorite brother!" Applejack said.

"I'm done with trippin' out on all these... colors. Ngh, I hate colors now!" Rainbow Dash said.

"Well, this is fun and all, but... I kinda feel a little... big, and tight." Pinkie commented.

"Well, that is simply too bad!" Shadow Hooves said. "I shall uncage my wrath upon Ponyville, and all of Equestria! Nopony will stop me, NOPONY! HA HA HA HA HA HA HA HA!"

Shadow Hoove's horn glowed for a moment, and she vanished in a bright flash.

"She's teleported!" Starlight said. "We need to catch her!"

"Wait!" Rarity said, awkwardly hopping her way over. "What about us?"

Twilight sighed. "Sorry, girls. But I'm afraid I don't know the reversion spell that will return you all to normal. Only by defeating Shadow Hooves will you all be back the way you were." she said.

"Just wait right here! Once we can reverse Derpy's corruption, you should all return to normal!" Starlight said.

"Okay..." Pinkie said, slowly rotating while still dangling upwards by her hind leg. "...not like some of us could go anywhere if we wanted."

With that, Twilight and Starlight took off, picking up Spike, who they hid in a patch of shrubbery nearby, leaving the rest of the Mane Six alone.

"Hm... well, actually..." Fluttershy began. "...it is kinda nice to just sit here. It's just so... peaceful."

"Glad you're happy, Fluttershah;" Applejack said, looking at her/his now-male body and crossing her hind legs. " 'Cuz this just don't feel... raht. This is just... embarassin'."

Rarity sighed. "Well this is just oh so mortifying..." she said.

"Oh, lighten up, girls! It's not so bad!" Pinkie said, before trying to press her abdomen. "But... this pressure really doesn't feel all that great; I feel like I might just pop! Plus, I'm starting to miss the ground!"

Rainbow Dash tried covering her lit-up eyes as both they, and the rest of her colors, were all changing.

"Ngh... I'm gonna lose it! I'm gonna freakin' lose it, man!" Rainbow complained. "I can't stand these blinding colors! I still see them when my eyes are closed!"

They continued to vent for awhile, during which time Twilight and Starlight were hunting down Shadow Hooves...

Well, Derpy seems to be enjoying the small sample of revenge she is getting at the moment... even if the Mane Six had nothing to do with her torment. Oh well, she's corrupted; what else do you expect? Anyways, I'll see about getting the next chapter uploaded as soon as I can! In the meantime, keep pressing on through the trials of the real world! Keep holding on...