The next day, the girls panicked, the amulet was permanently around Rainbow's neck and they had no idea how to get rid of it.

Fluttershy: What do we do?

Sunset: I dunno, I'm supposed to know how to keep Equestrian magic under control and I have no idea how to fix this!

Rainbow: Fix what? This amulet's too awesome, I don't see anything wrong with it.

Twilight: But, you're addicted to it. Maybe you should give it a break.

Rainbow: You kidding? Nothing bad happened since I found this!

Rainbow accidentally shot water at Rarity, who freaked out about her soaked outfit.

Rarity: Aah! Rainbow Dash, how could you?

Rainbow (nervously): Heh heh, sorry.

Twilight: See what I mean?

Rainbow: That was an accident, Twilight.

Sunset: *Sigh* We really need to get rid of that amulet.

A couple days later, invites were sent to all the Canterlot High students from Principal Celestia. There would be a summer festival at the school on Saturday to celebrate the beginning of summer and they needed volunteers to help get it ready. The Equestria Girls gladly volunteered to help out.

Pinkie: A Summer Festival?!?! Uh, yes please!

Fluttershy: Sounds like fun.

Rainbow: Yeah! I can show off my water skills!

Everyone glared at Rainbow Dash.

Applejack (sternly): Rainbow Dash.

Rainbow: ...On second thought, maybe I'll give it a teensy tiny rest.

Everyone arrived at Canterlot High. Sunset was unaware that the jewel fell out of her pocket.

Celestia: Thank you all for volunteering to help out. You can get started when ready.

The girls decorated the school gym in anyway they could. Disco Balls, streamers, balloons, ribbons, you name it! The girls also agreed that the Rainbooms would perform for the festival, so they decided to practice.

Sunset: Why don't we start with "Better than Ever?"

Applejack: Good idea!

Rainbow: Yeah! Can't wait to pony up!

The girls started singing.

https://youtu.be/AfeORp3dDYo

There was a time we were apart

But that's behind us now

See how we've made a brand new start

And the future's lookin' up

Ah-oh, ah-oh

And when you walk these halls

You feel it everywhere

Yeah, we're the Wondercolts forever

Ah-oh, yeah!

We are all together

Ah, ah, ah-ah-ah-oh

Now it's better than ever

Ah, ah, ah-ah-ah-oh

You can feel it

We are back

And I'm so glad that we're better

Better than ever

Wah-oh, oh-wah-oh

Oh yeah

We're better than ever

Wah-oh, oh-wah-oh

There was a time we couldn't see

Past the differences

That separated you and me

And it left us on our own

But now you walk these halls

And friends are everywhere

Yeah, we're the Wondercolts forever

Ah-oh, yeah!

We are all together

Ah, ah, ah-ah-ah-oh

Now it's better than ever

Ah, ah, ah-ah-ah-oh

Now that we are back on track

Yes, I'm so glad that we're better

Better than ever

Wah-oh, oh-wah-oh

Oh yeah

We're better than ever

Wah-oh, oh-wah-oh

Oh yeah

We're better than ever

Wah-oh, oh-wah-oh

Oh yeah

We're better than ever

As the girls were singing, they ponied up, they gained pony ears, wings, and tails. Sunset, however, noticed that Rainbow Dash didn't pony up as usual, which meant something wasn't right. She decided to investigate when they finished singing.

Sunset: Rainbow Dash, you didn't pony up like the rest of us.

Rainbow: What?

Rainbow studied herself head to toe, that was when she realized she didn't pony up. She got into a huge panic.

Rainbow: WHY DIDN'T I PONY UP?!?!?

Twilight: I think that amulet's affecting you.

Sunset: Where's your geode by the way?

Rainbow: Uh...

Since Rainbow Dash didn't say anything, Sunset touched her wrist to view her memories. She saw Rainbow Dash on the last day of school when she was on her way home and when she spotted the ominous comet and when she saw the amulet in her bedroom. She saw that Rainbow threw away her geode like it didn't matter and drove her attention to the amulet. Then, she saw her eyes glow purple which could be foreshadowing disaster.

Sunset: Rainbow, that amulet has to go.

Rainbow Dash took some time to think about it, she has been enjoying her new powers without listening to her friends and worst of all, she couldn't pony up. She wondered to herself, how could something so amazing be so dangerous?

Rainbow: Okay.

She tried to remove her amulet, but it wasn't coming off.

Rainbow: Sunset, how do get this amulet off?

Sunset (a little angry): That's the problem. The amulet doesn't come off.

Finally, Sunset lost her temper and yelled at Rainbow Dash.

Sunset: Ugh, I wish you never found that stupid amulet, Rainbow Dash! Ever since you found it, you've been so caught up in those powers that you completely ignored the rest of us and just stayed focused on yourself! So far, it hasn't come off and now it's affecting you and putting the rest of us in danger!!!! This is all your fault, Rainbow Dash!!!!

Rainbow: *Gasp!* (voice breaking) ...Uh...If that's the case, just continue the festival without me.

Rainbow Dash left the gym in tears.

Sunset: Rainbow Dash, that's not what I... *sigh*

Applejack: Just let it go, sugarcube. She just needs some time to herself.

Pinkie: I'm back!

Everyone turned to Pinkie Pie.

Twilight: Back from where?

Rarity: Where have you been all this time?

Pinkie: While you guys were busy talking to Rainbow Dash, I went back to her house and got this!

Turns out, Pinkie had rushed to get Rainbow's geode.

Sunset: *Sigh* Thank goodness! I'll give this to her when she feels better.

Twenty minutes later, the festival started, but Rainbow Dash still didn't return. Her friends were getting worried about her. Sunset felt guilty about what she said to her.

Pinkie: Why isn't Dashie here? She's missing out on all the fun.

Fluttershy: I'm getting worried about her.

Sunset: She's probably not back because I yelled at her earlier.

Twilight: Why don't we go and check on her to see if everything's okay?

Rainbow Dash was sitting outside the school, crying. While she was out there, she happened to notice a vibrating stone, she went to investigate and the vibration got stronger.

Rainbow (thinking): Is this the jewel Sunset was talking about? Better not, she did say something bad could happen, I can't even get this stupid amulet off! *Gasp!*

But suddenly, the jewel floated right into the empty spot in the amulet. The amulet changed from silver to black. 

Rainbow: Uh...what's happening?

The amulet glowed brightly, forcing Rainbow Dash off the ground. When her friends came to check on her, they saw what was happening and gasped in shock. It seemed like the amulet's power was more than Rainbow Dash could handle.

Fluttershy: Rainbow Dash?

Rainbow looked down at her friends, horrified. 

Sunset: *Gasp!*

Rainbow: Help...!

Rainbow Dash burst into tears as she was being pulled into the magic the amulet contained. The girls remained helpless and watch in horror as their friend was being corrupted by the dark magic. It was just like Princess Twilight warned Sunset, it was a huge transformation and, believe me, it wasn't pretty!

Rainbow Dash went through a painful transformation: 

Her sky blue skin turned purple, almost all her rainbow colored hair turned black, pink wings, the size of an eagle's, sprouted behind her back, a pink horn appeared on her forehead, and her magenta eyes turned blue.

At first, Rainbow Dash felt as if she was gonna be ripped apart, but then, she started to feel stronger, more powerful, like she could do whatever she could...