Dragon Dog
Later after the Mane Seven traveled to Equestria, puppy Spike stayed at Sci-Twi's house until they get back. He started to wonder how they're having fun in the pony world. Mingling with their pony counterparts, understanding magic and his dragon counterpart. Now he thought of it he races to the school.
At the portal, Spike talks to himself, "I know Twilight said to wait here, but I'll just do a quick visit. Besides, I wonder what it's like to be a dragon."
He jumps through the portal and out of the Crystal Mirror in the Castle of Friendship. As he looked at his reflection, he was still in his dog form. However, he developed dragon features similar to how the Mane Seven pony-up, such as given dragon spikes, tail and fire breath.
"I would call this dragon-up," he said.
In the library, both Twilights, Sunset Shimmer and Dragon Spike were searching through books trying to find out what caused the portal to keep travelers in their true forms. Sci-Twi was delighted meeting the dragon version of her dog again.
"You know," Sci-Twi said. "Last time we were here, I never mention how you make my Spike look cute as a little dragon."
"Speaking of which," Dragon Spike said. "I would like to meet him sometime."
"How about meet him right now," ask a voice.
Puppy Spike enters the library and delight to meet his dragon counterpart. Sci-Twi was amazed to her pup's part dragon form.
"I just couldn't help myself, Twilight," Puppy Spike said. "To see what it was like in this world and meeting ourselves as ponies or dragons. "
"It's okay, Spike," Sci-Twi said. "That was before we realize that the portal doesn't change us anymore. And more surprising seeing you part dragon. Just like how we pony-up."
"I know," Puppy Spike replied. "I called this a dragon-up. What do you think, Princess Twilight?"
"I'm impressed," Princess Twilight comment. "How you like to hang with my Spike? Because we're doing research on the portal."
Puppy Spike looks at Sci-Twi, who nods yes to him. Dragon Spike walks out with him and said, "I think we can get along just fine."
After a tour around Ponyville, the two Spikes caught up with each other, talking about their adventures in each other's worlds. Dragon Spike helps puppy Spike with his new fire breath and flies him around the castle.
"So, dragons go through a molting effect to earn their wings," Puppy Spike asked.
"Part of growing up," Dragon Spike said. "The last part is like how a caterpillar turning to a butterfly. When a cocoon forms around you until you hatch and feel good as new with wings."
"Cool," Puppy Spike comment. "Have you also met other dragons?"
"I have a couple who I'm friends with," Dragon Spike said. "There's Ember, the dragon princess who I helped become the new dragon lord. And there's also--" As he finished, they ran into... "Smolder."
"Hey, Spike," Smolder said. "And... another Spike?"
"Hey, Smolder," Dragon Spike said. "This may be confusing, but long story short this is me for another world."
"Really," Smolder asked. "Where you're a little dog that make you look cute."
"Thanks for that," Puppy Spike said.
"Smolder is a student at Princess Twilight's school," Dragon Spike explained. "She helped me understand the Molt Effect."
"And helped understand a little what dragons do," Smolder added. "Especially when some lazy dragon came by and pretended to be his father just to live the castle life."
"That sounds terrible," Puppy Spike comment.
"It was," Dragon Spike replied. "And we agreed to never mention his name again."
"Maybe got banished from Dragon Lands," Smolder said. "So, nice meeting you're dog self. I have to go catch up with my friends."
As she left to meet the rest of her friends, the Spikes head back to the castle.
Dragon Spike takes Puppy Spike in the throne room to show him the Cutie Map.
"This is a special map table," he explained. "We use this to look for friendship problems around Equestria. It makes their cutie marks glow and floats over where the problem is."
"How does know which ponies to summon," Puppy Spike asked.
"Depends on who's cutie mark glows," Dragon Spike said. "Sometimes it sends a few of us or other ponies. When it summoned me, my spikes glowed and made an image of my head. To solve a problem that I caused."
"And if it summons all of you," Puppy Spike asked.
"Only if it's a big problem," Dragon Spike said.
"You and your friends are amazing here," Puppy Spike comment. "And I had fun here."
"Me too," Dragon Spike said. "Guess you should head back to your world now. I'll let your Twilight know."
"Thank you," Puppy Spike said.
As they leave the room, the map suddenly starts to zoom in on the castle and shows an image of the Crystal Mirror with Sunset Shimmer, Starlight Glimmer and pony Trixie’s cutie marks over it.