Over night thick black clouds had rolled over the city. They threatened to spill but the rain hadn't come yet. Tony and Bruce stood on the roof of the Avengers Tower, arms crossed, heads titled back and stared at the sky.

"This is not the best day to be doing experiments on the roof Tony," Bruce warned.

"Absolutely not." Tony agreed. They stood for a few seconds more then Tony clapped his hands together and sauntered away. He approached a large piece of machinery that had been bolted in place. At the top was a satellite dish several feet tall and beneath it were screens and controls.

"But, you're going to do them anyway," said Bruce, hoping he was wrong.

"Hey, if Dr Banner can't take a little rain, then maybe I should do this with The Other Guy." Tony shrugged without looking back at him.

Bruce didn't even have it in him to sigh. He followed Tony to the large satellite dish and began to input the algortihm for their experiment.

"I mean, I can call Pepper and see if someone can bring us a couple of umbrellas," said Tony.

"Yeah because holding our own personal conductors on one of the tallest buildings in New York in this weather will end just fine."

"Well look who discovered sarcasm." Tony brought a hand up to one of the screens and used a button beside it to start scrolling through a list of numbers.

In truth the possibility of being struck were low. The dish had an attached lightning rod to prevent any damage. Lightning would by-pass all vital electronics. It had already been tested thanks to the God of Thunder himself.

"How reliable do you think the previous data is?" asked Tony.

"It's not so much reliability, more quantity," Bruce confessed. "It's no where near the amount I would like before going forward with test runs."

"But here we are anyway," said Tony.

"Here we are anyway," Bruce echoed.

"Well if anyone can make this work it's the Science Bros."

Bruce groaned. "Science Bros? Really?" Tony smiled out of the corner of his mouth.

The machinery was designed to detect changes in atmosphere and background radiation, specifically changes that happened when portals were opened. If the technology existed to create a portal then there was always the chance it could happen again.

The pair continued to take care of their individual tasks, occasionally switching places or peering at the other's work to share their thoughts. But after barely 20 minutes a chirping came from Tony's pocket. He slipped a phone out of his back pocket and read the screen. He sniffed and waved a hand. "I'm sure it's fine." The call went ignored.

Bruce raised his eyebrows at him when the voice of JARVIS echoed out of the small speaker. "Sir, Ms Potts has an urgent message."

"Can it wait? We're kinda doing important work here." Tony moved his hands as if to demonstrate to the dis-embodied voice.

"Ms Potts said that if you ignore her next call she's locking you on the roof." Right on cue the phone started to chirp again. Bruce noticed how quickly Tony answered it. He walked away as he spoke with Pepper. The speaking turning quickly to arguing and Bruce did his best to pretend he couldn't hear.

It soon became apparent that Bruce would be working alone for a stretch of time. Tony finished the call and took a moment to tap the edge of the phone against his chin. "Turns out it was pretty urgent."

"Should I worry?" asked Bruce.

"Nah, just means you're flying solo for a while. Sorry buddy. Unless you want to pick this up again tomorrow?"

Bruce shook his head. "It's fine, go, go." Tony jogged away and Bruce was left alone to work.

A further 20 minutes passed and something else began to make a noise. Confused at first, Bruce checked his pockets for a phone. Mid-way through checking he realised the beeping was coming from the apparatus in front of him.

He twisted one of the screens and spotted the read-outs reacting to something. He quickly brought up the data gathered during the battle of New York. To his relief the changes were far smaller and not quite similar enough to suggest the same thing was happening. However something was happening.

Bruce took a couple of steps away and titled his head back. All he could see were dark clouds. Except there was movement. It was difficult to tell whether he was seeing something or just looking at more clouds.

Then he heard a roar. It sounded like a lion was roaring while someone scraped metal sheets together. There was definitely something up there, directly above him and it was getting bigger. No, not bigger. It was getting nearer. It was falling.

A large black creature was twisting in the air and getting closer by the second. Bruce didn't get the chance to clear the area, instead he threw his hands up and as he did they stretched and grew. His skin faded to green and his clothing shredded, the stitching snapping.

The creature made one last shriek and fell into the hands of The Other Guy. The Hulk allowed the weight of the thing to bend his arms downwards, breaking its fall. The Hulk grunted and let the creature flop out of his arms and on to the floor in a bundle of limbs.

It was scaled like a reptile and had two large leathery wings that revealed themselves as it rolled over with a yowl. There was a long tail too with what looked like fins on the end. Except one of the fins was out of place. Rather than black it was bright red.

Behind the Hulk, the beeping of the machine slowed to a stop. He twisted around and narrowed his eyes, looking to the screen. "Portals closed," he grunted. The creature finally righted itself on to four legs and straightened its wings.

This was a dragon, or perhaps an extra-terrestrial creature that looked like a dragon. Whatever it was, it didn't belong on Earth. The dragon stared at the Hulk with large cat-like eyes and arched its back. Teeth were bared as it stalked a circle around him.

Hulk gave another glance at the red fin on its tail and noticed what looked like a painted symbol. It wasn't a natural fin, it had been handmade and it was broken. Hulk tried to grab the dragon by the back of the neck so he could get a better look. The Dragon dodged his hand with hiss. Hulk tried again. And again. Each time the dragon weaved and hopped out of the way.

One last grab, this time he pretended to aim for its leg with the left hand but instantly switched at the last second and aimed for the base of the tail with his right. The Dragon yipped and cried, not at all happy with someone holding on to its tail like that. But when the Hulk had something, it was impossible to escape.

The dragon settled for climbing up the Hulk's large frame and biting him wherever he could reach. Hulk ignored what felt like mere nibbles to him and jumped off the roof and down to the balcony several floors below. The dragon dug its claws and stiffened.

They landed with a heavy thud and the Hulk continued on into the Avengers tower, more specifically the open-planned common room, the only place large enough to accommodate a Hulk and a Dragon. As soon as they had hit solid ground, the dragon continued to crawl and squirm around the Hulk's torso.

But once they stepped inside its ears went up and he scanned the room. The dragon hopped off and tried to run back outside. Its feet slipped on the smooth wooden floor, unable to so much as stall the Hulk. The Dragon was dragged for almost 10 feet when he decided to try flying instead.

The common room had a bit of everything. A small kitchen and bar for making food, an enormous 12-person meeting table, sofas, even a work-bench with some of Tony's equipment on it and an elevator that went "ping" right as the dragon was madly flapping in mid-air.

The doors opened and Clint was there, staring at the strange event happening in their common room. Without a word he leaned towards the elevators buttons and pressed for another floor. The doors closed again.

Hulk slid his free hand under the dragon's belly while it was still on the ground and lifted it carefully on to the meeting table. Worn out by all the struggling, the creature let itself drop to the tabletop and sighed. There was peace for all of 5 seconds before the dragon started sniffing something. It lifted its nose as it smelt the air and its eyes opened, looking for the source.

On the edge of the table was a stack of pizza boxes, the top box was open, revealing half of a pepperoni pizza. The Dragon scrabbled forwards, trying to inch its way closer. At last Hulk let the poor thing go and it leapt forward, knocking boxes and slices of pizza everywhere.

The Hulk scratched his head as the Dragon gulped down every scrap of food it could find. With the creature pre-occupied he could give the fins on its tail a closer look. The red fin was made of cloth and wooden poles with a leather belt that kept it attached at the tail. The poles looked like they might be snapped and a section of the cloth was ripped.

In addition to the fin there was what appeared to be a saddle. It was made from leather with stirrups and handles. Stitched at the front was a name. "Toothless." Perhaps that was the creature's name?

Something began to make a noise. It was musical but the sound was tinny. The Hulk frowned when he felt an odd vibration against his thigh. He raised an eyebrow as he realised the Stark-made shorts came with pockets. He poked a finger inside and managed to slide out a phone that would most likely break if he applied any sort of grip.

The screen displayed Tony's name and grinning face. The Hulk grumbled and poked at it with his other finger, answering the call.

"Brucey, disaster has been averted and that means I'm coming back if you're still on the roof." The Hulk grunted. Apparently Tony didn't pick up much of a difference. "I'll take that as a 'I'm still working.' Be there in 5."

The Hulk looked up to see the Dragon eyeing the phone with curiosity. It titled its head to one side and then to the other as it made another unusual sound. "I don't like phones," he said simply. The Hulk threw the phone in the vague direction of the table but it hit the edge and clattered to the floor.

The Dragon hopped over to it and with a dainty claw, pressed the screen. It lit up and the creature began to make an odd sound as if imitating a conversation. It jumped back when a voice came from the phone's speaker again.

"Yeah, you need something big green?" The Dragon crouched down and sniffed at the device and it was then the Hulk had an idea.

"Pizza."

A few minutes later and Tony arrived complete with a pair of pizza boxes in his hand. He took one step into the room and had to take a moment to assess what he was seeing. The Hulk could practically see his mind trying to process what was happening when Toothless raised his ears and ran towards Tony.

Tony instinctively lifted the pizzas in to the air but they were quickly knocked from his hands with a swift head butt from Toothless. This time however the box wasn't open for easy access. It had landed on the floor and Toothless kept nudging at it in an attempt to get inside. The result being a large black dragon pushing pizza boxes across the floor at speed.

"What the..." was all Tony could manage. His hand went to his head and he pushed his fingers through his hair. "What is going on?"

"He's Toothless. And he likes pizza." The Hulk shrugged.

"I didn't know when I said "big green" I was actually talking to the man himself," said Tony.

"Portal open, he fell through. Portal closed again and he can't fly. His fin's broken."

"Well then, let's give it a look."

Toothless had managed to corner one of the boxes against a wall to stop it from moving and had pried it open with a claw. He munched away as Tony approached his tail for a closer look.

He crouched beside the fins. He stroked a finger over the red material and then tested the wait of it in his hand. "Materials got a couple of tears and most of the supports have snapped but it's a pretty basic design, shouldn't take long to fix. I'll just need to take the fin off first."

Tony grabbed the strap holding it in place and began working the buckle to untie it, unaware that Toothless had tensed. The dragon lifted his head and twitched his ears. Unimpressed with yet another invasion of his space, he flicked the tip of his tail, whacking Tony in the face and throwing him backwards. He landed on his back with a grunt and squirmed on the floor, his face scrunched up in pain.

With Tony vulnerable the dragon took his opportunity and span on the spot to land in an aggressive stance and roar. The Hulk strode towards the pair and placed himself between them. He folded his arms and frowned at Toothless as if to scold him. "We help."

Toothless flinched for a moment. The two stared each other down for a few moments before the dragon relaxed a little. He tilted his head at the big green monster, perhaps in understanding.

The dragon lifted its front paws to walk on its hind legs. It was still a couple of feet shorter than the Hulk. Toothless rested his front paws on the hulks arms and yowled up at him. He then leapt on to his shoulder and hopped back down to the floor behind him. Tony was still on the floor and starting to look worried.

An unusual sound erupted from the dragons throat as he lifted his head and bared his teeth. It wasn't unlike laughter and the creature didn't appear quite so threatening anymore. Toothless then sat up and looked away like a proud cat before allowing his tail to lie at Tony's feet.

With a tad more hesitation than before Tony worked at the straps keeping the red fin in place and removed it completely. The second it was off, Toothless wormed his way back to the unfinished pizzas.

Tony was on his feet again, inspecting the thing in his hands. "Nice bit of kit. Wonder where it came from?" He was about to leave the room with it when he heard Toothless whine.

"Work on it here." Hulk ordered. Tony raised his eyebrows, not used to getting orders from the big green guy but did as he was told. He took the elevator to his lab and returned minutes later with a metal toolkit and an armful of materials.

"Is this going to be my job now? The mechanic that fixes junk from other dimensions?" Tony set the toolbox on the table along with a pile of wood, rope and metal rods. "JARVIS, a little music please."

A drumbeat vibrated through the air from hidden speakers. Toothless pricked up his ears and began stalking the room to try and find the source of the noise. The Hulk sat on the floor with his hands on his knees and watched the creature. With no success in finding the source, Toothless gave up and instead began to to bend his legs and bob his head in time with the beat.

Another "Ping" came from the elevator and Clint stood there once again. "Just had to make sure," he said before hitting a button again and vanishing from view.

An hour later and a strange gathering was happening on the roof of Avengers Tower. A dragon, a green monster and a man in a metal suit were making preparations. The fin was fixed and back on Toothless and Tony, now in the Iron Man armour, was playing with the apparatus he and Banner had set up.

"So there's good news and bad news," said Tony. "The good news is that whatever portal Dragonheart here fell through will open up again shortly, so if he can fly back through, he can get home." Toothless titled his head as if paying full attention to Tony's words.

"The bad news is that the portal is unstable, meaning that once he's through, we're left with the problem of how to close it for good. But let's deal with problem number one first, getting you up in the air buddy." He stared at the dragon through the open flap in his helmet.

The Hulk bundled Toothless in his arms and with little warning flung the poor creature directly upwards. As he ascended the creature was nothing more than a black bundle of limbs and wings, but the second he began to fall again his wings opened, his tail straightened out and he tried to glide.

At first the dragon seemed to soar smoothly, then he flapped a couple of times and began to falter. A gust of wind threw him off balance and Toothless started spiralling back down.

Loud beeps sounded from the apparatus. Tony desperately looked from one thing to another. He pointed to the falling creature and shouted to the Hulk. "Keep him in the air!"

Tony closed the Iron Man helmet and JARVIS spoke to him. "Sir, the portal will open in about 15 seconds and remain open for about 1 minute." He could see a read-out transmitted from the apparatus to his HUD. Above them the black clouds formed again.

"Is that all the warning you're gonna give me?"

The Hulk was already moving. He leapt threw the air and grabbed Toothless. The pair landed heavily on the next roof over. Without missing a beat, the dragon was thrown into the air again. This time Tony flew up with him.

Toothless rolled through the air, making it impossible for Tony to get a good look at the red fin. "You need to keep your tail still." Toothless yelped with no sign of stabilising so Tony waited for another spin and flew underneath him. He put his arms up to grab the dragon by his belly.

The pair flew upwards and with Tony's help Toothless was able to spread his wings again. "Okay buddy, I need you to take over so I can see that tail." The dragon seemed to understand and began sweeping his wings up and down. The second Tony felt him pull away he repositioned himself to see the fin.

Below them the Hulk bellowed. It was a warning. "Sir, the portal is open," came JARVIS's voice.

"Once again, thanks for the warning!" he shouted. Tony lightly held the dragon's tail with one hand and with the other made adjustments. One of the joints had failed to move, preventing the fin from opening the entire way. A quick tug on one of the metal rods solved the problem.

Tony fell away and with a sudden thrust of his boosters was beside Toothless. He was going to see this through to the end. "Sir, if you stay on this trajectory you will hit the portal."

"Noted, JARVIS."

Black fog hit the pair of them and in less than a second they were clear of it again. Toothless appeared to cry out in joy. He flew backwards to flash Tony a smile, his tongue dangling out as if in thanks. He arched through the air and vanished below a white cloud.

Tony cut the thrusters and allowed himself to fall back through. Just as he was about to hit the portal he spotted Toothless plough back through the cloud and up in the air. This time with company. Someone was on his back, riding in the saddle and whooping for joy.

The black fog blocked his view before he could see anything else and suddenly he was back home again.

The Hulk was back on the rood of Avengers Tower, waiting for him. Tony landed gracefully in front of him and removed his helmet. "The little guy made it back home. And by the looks of things, he found his friend too."

The Hulk nodded and his lips hinted at a faint smile.

...

A.N. : I wrote the first half of this ages ago so I figured it was time to finally finish it. If you liked it, why not take a look at my other cutesy Avengers cross-over One Shots?

And if you reeeally enjoy my writing, why not check out my dystopian fantasy book? Links are on my profile page.