The so-called "Grogar" occured to be Discord in disguise when his magic was taken away into Bewitching Bell.
Now this evil trio – Cozy Glow, Lord Tirek and Queen Chrysalis are the biggest danger to Equestria – especially since they possess this extremely powerful artifact capable of stealing other creatures' magic they've used on Discord, who was now in Canterlot, warning Mane 6 and Princesses about incoming danger.
The group left Grogar cave with smirks on their faces.
“So, where should we strike first?” Cozy Glow asks while holding Bewitching Bell.
Chrysalis giggles ominously and says – “everywhere”
After that being said, each one headed different directions - Chrysalis went to the School of Friendship to take her revenge on its headmare - Starlight Glimmer, the same mare that encouraged Thorax to share love instead of stealing it, which made him change to good version of changeling and so other changelings did the same. This event led Chrysalis to be dethroned and got Thorax to be their new ruler.
When Chrysalis was getting to her target pony, she came up with a lot of ideas how she could take her revenge on Starlight, all of them were cruel and simply demeaning.
Tirek decided to strike from southwestern side of Canterlot as he knew he'd meet Pillars of Equestria. He also was aware, that even when he would fight legendary ponies, they are no match to his power after getting his part of magic from Bewitching Bell.
Meanwhile Cozy Glow, in a form of alicorn, was holding Bewitching Bell while heading straight to Canterlot Castle to assassinate future ruler of Equestria - Twilight Sparkle. But while she was getting there, some thoughts were going across her head. These thoughts were ideas what she will do after Twilight would be defeated, but soon they were replaced by qualms and wanted to back off from it.
"Am I doing the right thing?" - Cozy Glow said to herself - "Is that what I really want - vengeance and unnecessary casualties?" - she continued. She immediately stopped after saying the latter phrase and was just hovering in the air before she landed and looked down.
"I can't do this! No - I mustn't do this! Not after Twilight showed me her faith in me and let me be her assistant and I awfully betrayed her and all of Equestria by trying to get rid of all its magic!" - tears started to fill Cozy's eyes
"I'm pretty sure she thinks I'm beyond any redemption and I shall show her she's not right about that! I will help them!" - she tried to suppress her tears, but failed miserably - they flowed through her cheeks. She wiped them with her right foreleg. But she quickly realised one thing - Tirek and Chrysalis were coming to Canterlot!
"Oh snap! My two allies, or rather ex-allies, are now on their way to Canterlot! I must hurry up and warn the princesses and Twilight! Maybe it's not too late!" - with that being said, again to herself, Cozy Glow instantly flew up and headed to Canterlot as fast as she could.
"I have enough power to support them in this fight!" - she thought
Meanwhile Twilight, her closest friends - Rainbow Dash, Rarity, Applejack, Fluttershy, Pinkie Pie, Spike, along with Princess Celestia and Luna, a few royal guards and traitor, who is responsible for all that mess, in the day of Twilight's coronation to be the new ruler of Equestria - Discord.
They were getting ready for the raid of three extremely dangerous villains. Despite the fact all of them was prepared everypony was anxious what will happen during this raid. Mainly because they were able to seal away Discord's magic and could use it for their own advantage.
Twilight Sparkle was standing on the throne platform, giving motivational speech to ponies gathered in throne room.
"And I can't do this alone, but I'm not afraid" - Twilight said, closing her eyes "Because with friendship as our armor and teamwork as our power, no pony can ever bring us down" - she said flying, with her hooves spanned
After she said that, something crashed with huge impact force into the stained glass, closest to throne room door, shattering it into tiny pieces, making some object inside red force field enter the room.
Soon the force field disappeared, revealing mysterious "object".
It was Cozy Glow, carrying Bewitching Bell.
Twilight frowned in confusion.
"Cozy Glow? You're an alicorn?" - she asked
"Yes, it's me and indeed I'm an alicorn" - Cozy confirmed. Everyone shot daggers at her and some guards began approaching her.
"Wait, I'm not here to fight. I'm here to warn you and help!" - Cozy yelled, which made guards stop. - "Here, take this bell; it might be useful later"
With that being said, Cozy used her alicorn magic to levitate Bewitching Bell and gave it to Twilight. Everyone wore a frown, that was a mix of confusion, shock and curiosity, why Cozy Glow wants to help them.
Twilight slowly approaches Cozy Glow.
"Okay, I'm surprised, to say the least, but how do I use this thing?" - Twilight asked, pointing at the bell being carried with her magic.
"Oh, huh, should've also given you this" - Cozy slightly embarassed took two sheets of paper hidden in her curls, which were pages ripped from the book used to cast the spell to take "Grogar's" magic.
"Thanks, but...why do you want to help us?" - Twilight asked; she still couldn't believe what was happening.
"I-I reminded my past actions, with trying to wipe out all magic in Equestria and tricking you to go to Tartatus" - Cozy's voice began to crack - "I just feel awful for everything I've done. I want to apologize you all for it, though I don't expect your forgiveness"
Everyone, even princesses and Discord gasped. It definately wasn't what they would expect - malicious, vicious, yet adorable-looking villain come to them, apologize for her actions and even support them.
Shortly after that, Twilight got out from shock and put her hoof under Cozy's chin and gently lifted it, making the filly look at her face.
"Well...I don't know what to say" - Twilight said still unsure, but soon after her mood turned to happiness - "but I'm proud of you. I thought you were beyond redemption and was rotten to the core, but apparently now you understood your mistakes and want to be good once again" - she continued, but soon said somberly "however I still have to take away your alicorn magic"
Cozy Glow looked deeper at her former teacher's eyes and answered:
"I understand" but quickly added "and by the way, Discord's magic is in this bell, I'm sure he wants it back", which made Discord smile.
Twilight took her hoof from her chin, looked at sheet of paper and cast a spell on Bewitching Bell. Then Cozy Glow was no longer an alicorn and Discord got his chaos magic once again.
"Sorry you had to wait that long for your magic" - Cozy said, avoiding eye contact with Discord
"It's fine" - he answered and snapped his fingers, making Cozy appear under his left arm - "besides, that's just amazing that you want to be our little good Cozy once again" - Discord said playfully and booped her nose, which made it scrunch up and Cozy giggled from the tickling.
Everyone seemed to be happy, especially the god of chaos.
"But we should get ready!" - Cozy Glow exclaimed - "Tirek and Chrysalis are on their way to this place, and are more powerful than before, because they also possess their part of magic that was inside this bell"
That sentence made everyone worried again.
"Don't worry Cozy" - Twilight reassured her and everyone else - "we have high chances to win with them. Even if they are strong. And if you really want to help and show you're willing to reform and redeem yourself, you can go with us".
"I'm with you" - Cozy said, smiling and squinting her eyes.