Rainbow Dash and Twilight were freaking out over Twilight's body now having some physique. Then Rainbow Dash remember what Spike said. "Twilight, is this the result of that transfusion you've been through?"
"Wait, you know about that?" Twilight asked.
"Yes. Spike told me. It's no wonder you were fascinated with Spider-Man." Rainbow Dash said.
Twilight blushed. "Yes. I did got a transfusion from Spider-Man but why didn't this happen before the Friendship Games?" She asked in panic.
"I don't know." Rainbow Dash said.
"I think I do." Spike said. "Twilight, remember your healing power off the power kicked in after transfusion?"
Twilight remembers it. And she also remembers that dream she had of seeing another version of herself with a Spider-Man costume. "I think I understand." Twilight tries to figure out. She then tried wall climbing. She places her hands on the wall and then placed her foot on the wall and then she started moving carefully to the ceiling.
Rainbow Dash was surprised. "What is happening?" She asked in shock. "You can't be Spider-Man, can you?"
Twilight then dropped down to the floor. She landed on her knees. "Maybe. It seems Spider-Man's blood did gave me his superpowers but they must've been dormant. And after realizing I used my Midnight Sparkle magic, it must've altered my DNA and it awakened my spider powers."
"So, because of the magic Cinch made you use during the Friendship Games, it caused your spider powers to activate?" Rainbow Dash suggested.
"That seems to make sense. I didn't tell anybody about my transfusion in New York, cause I didn't wanna worry my brother or my sister-in-law." Twilight explained.
"Well then, what are you going to do now?" Rainbow Dash asked Twilight.
"Well, I had a dream that Midnight Sparkle tried to control me, but she was vaporized by a version of me in a Spider-Man costume. "I know what I'm going to do." Twilight said as Rainbow Dash listen. "Ever since the Friendship Games, I've felt nothing but fear and guilt cause I almost destroyed our world to get to Equestria. I stole magic from you, Sunset, Applejack, Fluttershy, Rarity and Pinkie Pie. I believed being Midnight Sparkle was... Unforgivable. But maybe there is a way for me to forgive myself. I am going to use my powers for good. Help people, be a real hero. Redeem myself for my actions as Midnight Sparkle."
"You want be a superhero to forgive yourself for what happened at the Friendship Games?" Rainbow Dash added up. "Being a hero, would.be your coping mechanism."
"It's the only way I can forgive myself Rainbow Dash." Twilight said.
"Very well Twilight, if your going to be a superhero, then your gonna need some training. Thankfully, Saturday today. And I'm gonna train you." Rainbow Dash said.
"You really do that for me Rainbow?" Twilight asked.
"Your my friend Twilight. And I forgave you already. But if you really wanna forgive yourself by becoming a superhero, then you won't face it alone." Rainbow Dash said patting Twilight on the shoulder.
Twilight hugged Rainbow Dash. "Thank you Rainbow Dash. You really are a loyal friend."
"That's what Sunset and pony you said." Rainbow Dash said. "Now let's get started.",
Later...
At the fields of Canterlot High, Rainbow Dash quickly ran helped Twilight learn how to adapt to her new spider powers. She tried running, her agility and speed were incredible.
Next, Rainbow Dash tested out Twilight's strength by making her karate chop some wooden planks. She was swift and managed to chop them all in half. It made Rainbow Dash very shocked. 
Rainbow Dash then tried acrobatics since Spider-Man is very athletic. She tried to see if Twilight can jump on top of a football goal post. Twilight ran and then she leaped in the air very high, she grabbed the middle of the goal post and did a 2 loops on it and then jumped all the way down to the field. Rainbow Dash was impressed.
Now comes the final step in Twilight's training. Rainbow Dash took her to a local gym where she exercise her legs. There was a boxing ring that Twilight can use to practice fighting. She was already in her Spider-Man onesie anyways. "Okay Twilight, so far, you have proved your agility. Now we'll see how well you are in a fight." Rainbow Dash said. "Now, I'm gonna try to attack you with my punches, let's see if you're fast enough to dodge."
Rainbow Dash charged at Twilight with a blow, and to her surprise, Twilight dodged it with ease. It even shocked Twilight. "Whoa." She didn't know how did that happened.
"That was good. For beginners luck." Rainbow Dash said. "Now, let's try again."
Rainbow ran at Twilight with a few more strikes, and Twilight managed to evade them. "Look, I don't know how that just happened. But I had this buzzing in my head that causes my reflexes to kick in."
"You must have what Spider-Man has, his spider-sense." Rainbow Dash exclaimed.
"That's true." Twilight said. "Spiders can sense and detect anything coming their way."
"Awesome." Rainbow Dash said. "Now time for the real fight. Try to knock me out. But I should warn you, I won't go so easy."
"Alright Rainbow. I'll do my best." Twilight said.
Twilight runs at Rainbow Dash swinging her fists around, Rainbow's sport skills makes her fast and she dodges Twilight's punches. Rainbow Dash then tries to attack Twilight with some kicks and flips. Twilight didn't know they were using their legs, so she too did some flips and jumps over Rainbow Dash and back hit in with her elbow. Rainbow flipped back but it was exciting that Twilight was catching up with her now. She landed a punch on Twilight's waist and kicked her in the face, forming some combo moves.
But then, something unbelievable happened...
Twilight took off her gloves tried a little something she picked after testing out her acrobatic skills. She blast something out of her hand and it stick to Rainbow Dash's arm. It was a light blue glow. But it looked like a web. Rainbow Dash was shocked. It would seem combining the spider blood and the magic of Midnight Sparkle didn't just awaken Twilight's spider powers, but it made her midnight magic form some sort of magical webbing. She yanked Rainbow Dash right to her and punched her really hard on the face, knocking her out.
A few minutes later...
Rainbow Dash woke up and she was feeling a bit dizzy. "So, you can make magic webs?" She asked.
"Yeah. I can't believe it happened." Twilight said. "I figured it out when I saw my hands and my wrists glowing. Maybe because of my spider-blood, it mixed with my midnight magic, giving me magical webbing."
"Wow. That sounds cool. And you managed to knock me out with your spider strength." Rainbow Dash said. "Let's keep practicing."
Over the next few hours, Rainbow Dash as taught Twilight how to fight well, she runs faster, jump higher, shoots her magic webs. Although, swinging was a hassle. But Twilight had managed to adapt very well.
The next day...
Rainbow Dash was riding Twilight's back as she wall climbs to on top of CHS. She handled the weight and pressure very well. "Congratulations Twilight, you have finally fulfilled your training." Rainbow Dash said, giving her the thumbs up.
Twilight was so happy. "Thank you so much Rainbow Dash, I really appreciate it."
"Now, all we need is a superhero costume for you." Rainbow Dash suggested.
"Oh, I already had one planned out." Twilight said. She shows a picture of a pink onesie she ordered from eBay that comes with a spider emblem on it. "It came yesterday after we finished training at the gym."
"A onesie, really, a baggy pink onesie?" Rainbow Dash asked, raising a brow.
"Spider-Man and maybe other superheroes like him, they wear spandex, and pretty much, it's like their wearing nothing at all." Twilight said. "So I need something loose."
"Alright Twilight. Let's swing to your house and see this onesie." Rainbow Dash suggested.
Later...
At Twilight's house, Rainbow Dash sees Twilight putting on her costume. She even had a custom Spider-Man mask and some pink gloves. "Rainbow Dash, say hello to the friendly neighborhood Spider-Girl!" Twilight exclaimed as shows herself in her complete costume.
"I got to say Twilight, it does look good on you." Rainbow Dash said. "Well, I gotta get going. So go out there and show world there's a new spider in town."
Twilight hugged Rainbow Dash. "Thank you for everything Rainbow." She said.
And so Twilight jumped out from her window and swing out into the city, as Spider-Girl.
To be continued...