Twilight became more and more frustrated as she turned through the pages of one of the old spellbooks she had dug up. She needed to find an new spell for the upcoming magic expo but so far her search was to no avail. According to this years rules it needed to be something that was both unmastered by modern unicorns and took place over a period of time, each contestant being required to log the effects of the spell as it went on. There was an additional rule that if a live pony was involved in the experiment they couldn't be harmed.

For the life of her she couldn't find anything new though! She let out a grunt of frustration and swatted the spellbook to the floor. A few silent moments were spent with her head on the desk before she levitated the book back up to her, she was about to close it when a few particular spells on the current page caught her attention. Lined up in a column were spells about slowing a pony's metabolism, increasing appetite, and converting the current content of a pony's stomach into fat to be stored later thus emptying their belly for further eating. It didn't take long for her to figure out that these were weight gain spells.

This definitely fell into the category of what she was looking for, and it seemed like a relatively harmless experiment. It would require an actual pony subject though. Twilight initially thought of using herself, she was close to normal weight with maybe a few pounds over, but the experiment would be much better if she started with somepony who was especially small or thin. Who did she know that would work fell this? Rainbow Dash! The athletic Pegasus was the lightest of all of Twilight's friends, and the final results of these spells would have a greater contrast on her than any other subject Twilight could get.

She shook her head, was she really considering using one of her best friends as a guinea pig for this? She knew that Dash probably wouldn't take well to the idea of being fat, and Twilight knew there were several things wrong with secretly fattening a pony. On the other hoof though, it was only a temporary experiment. She was sure that she could find a spell to reverse whatever weight Dash gained when it was over. Plus, it wasn't like it would hurt Rainbow or anything. Dash's next competition wasn't for a few months, Twilight was sure she could wrap this whole thing up before her friend's life was really affected in any way.

"Twilight, you almost ready to go?" Spike's voice called from downstairs, breaking Twilight's thoughts.

"Be there in a minute, Spike!"

She couldn't believe she almost forgot about Pinkie's party that was happening tonight. All her friends would be there. It would be the perfect chance to give these new spells of hers a trial run. She could decide afterwards if she wanted to continue with the experiment or not. She tore the appropriate page out of her spell book and hid it in a saddle-bag she was taking with her before heading out.

As typical of a Pinkie party, it didn't take long for things to get into full swing. Rarity was on the opposite side of Sugarcube corner, trying to convince Fluttershy to try her latest dress designs. Spike as expected was very nearby, hoping to grab Rarity's attention whenever he got the chance. Pinkie was bouncing back and forth between different parts of the room making sure everypony was having fun. Meanwhile, Rainbow Dash and Applejack were getting into one of their arguments over who-knows-what.

Normally Twilight wouldn't pay much attention to the squabbles between AJ and Rainbow, but her interest was caught when their arguing turned into talk of a food competition. The perfect opportunity!

"I'm tellin' ya Rainbow, ya can't beat a country pony in a pie eating contest. It just can't be done," boasted Applejack.

"Oh yeah? Well there's a first time for everything. Bring it on, unless you're scared," replied the rainbow haired Pegasus.

"Alrighty then, ya asked for it. Pinkie, bring us the pies!"

Before long Rainbow Dash and Applejack were seated at a table, with a mountain of pies in between the two of them. Both mares had a look of sheer determination, eagerly awaiting the start of the contest as Pinkie began a count of three. All the others had gathered close around the table to watch the upcoming contest. Twilight had taken up a strategic position in the back, where she could see what was happening and put her plan in motion without being caught. She took a final look at the spell page she brought with her before charging her horn and casting two precise spells on Rainbow Dash to prepare her for the contest. One to spike Rainbow's appetite, making sure she'd consume plenty high calorie pies. The second was to slow her metabolism and make sure most of said calories would be converted to fat.

As Pinkie's count hit zero both competitors grabbed the nearest pie and began eating like animals. The first pies quickly disappeared, followed by the second ones, and the third. The delicious flavor of the pies only encouraged the two competitive friends to keep going. Flavors of apple,blueberry,pumpkin, and more ensured that the ponies consuming them would be pushed forward if for no other reason than to keep indulging in the amazing tastes.

However, sheer determination and great flavors could only work for so long. Around the fourth set of pies both Rainbow Dash and Applejack were beginning to slow down. Neither showed signs of giving up all together though. Twilight was keeping a special eye on Dash's belly. Before the contest began it was completely flat, but as the competition went on it was beginning to bulge slightly and become more taut as she stuffed herself beyond usual capacity. Twilight had to suppress a grin as she pulled her third spell out of reserve. In a matter of seconds Dash's belly returned to it's original state, and she now had the entire space of her stomach to fill up again. All the food that was occupying it was now gone, at-least until later when it would undoubtedly appear on her figure instead.

The effects of Twilight's spell gave Rainbow a second wind, and she soon began to surpass Applejack in sheer number of pies eaten. Although, while Applejack was slowing down more and more as things continued, Rainbow seemed unfazed and continued eating at a rapid pace. The cyan Pegasus' gluttonous zeal shocked everypony in the room, save for Twilight. The contest drew on longer than any member of the group expected, but at last it came to an end as Applejack dropped her latest pie and declared defeat.

"I'm done ya'll. Congrats Rainbow, ah don't know how ya did it...." Applejack's words were mixed in with groans, and it wasn't hard to see why. She was extremely bloated, with her belly poking out large and round from the excessive amount of food stuffed in it. Twilight was tempted to help her poor friend using one of her nifty new spells, but decided it was best to stick with one test subject for now.

Rainbow Dash wasted no time in celebrating, letting out a victorious shout before responding, "I knew I could win. That was pretty fun though, we should have a rematch sometime"

Applejack shook her head, "Maybe sometime down the road, but ah don't even want to think about any kind of food right now. I think I'm just gonna lay back and rest some of this off"

Dash shrugged in response, "Suit yourself, I'm going to keep on partying," with that Dash made her way over to a nearby table and grabbed up a piece of chocolate fudge cake. She quickly scarfed the delicious morsel down with greed. Rarity made her way over to the table and gave Rainbow an incredulous look.

"Dahling, how can you still be hungry after that contest?"

"I don't know, I had some pretty heavy work-outs today. Those can really make you work up a huge appetite. Don't worry about it."

As the party continued onward Twilight made sure to mingle regularly with all her friends. Meanwhile, whenever an opportunity presented itself she'd cast the appropriate spell on Rainbow Dash to make sure she'd keep consuming all that fatty food which had been laid out for tonight. It wasn't until things started settling down that Twilight decided to give her Pegasus friend a break, and allowed her to finally feel a full and content stomach for the first time since the evening started. Most of the group was too tired or stuffed to feel like going home, so they unanimously decided to stay the night at Sugarcube Corner. Sleeping bags were laid out and everypony laid down for the rest of the night.

Twilight happened to find herself sleeping not far from Rainbow Dash, and when her friend wasn't looking she took a long stare at Dash and tried to ingrain a mental image of her current figure to compare with her appearance down the road. It was certain to change sooner rather than later, and considering that Dash had consumed days worth of food in one night it was likely that Twilight would have some early results by the very next morning.

Author's Note

I originally started posting this fanfic on DeviantArt, but decided to expand here as well. Constructive comments are welcome.