Disclaimer: Not mine.
Harry caught Sam as the poor hobbit tripped over a skeleton lying in the corridor they were walking down. At least Gandalf was sure about where they were gong still, he did not fancy getting lost under the mountains. The silent, empty halls made him shiver, they should be filled with life and light as dwarves went about their lives. How many had come to try and reclaim their ancient home and now lay dead around them? They came out of the corridor into what felt like a massive room and the light from Gandalf's staff increased, revealing gigantic stone pillars lining the cavernous room. It was incredible! He looked around in awe but then started as Gimli let out a noise of grief and darted into a small side room. The rest of the company followed to find Gimli kneeling in front of a massive stone sarcophagus. "Here lies Balin, son of Fundin, Lord of Moria." Gandalf read the dwarven writing even as Gimli sobbed. Harry bowed his head in a silent prayer for the dead and then moved to scout around the room, it was obvious the surviving dwarves had made their last stand in the room.
"We need to move on, we cannot afford to linger." Boromir murmured, looking around nervously. The room would only serve to trap them if they were discovered inside. Instead of answering Gandalf gently pried an old book from the skeletal hand of one of the fallen and flipped to the last pages, reading aloud the horror they had lived. None of them noticed Pippin reaching out to touch the skeleton that rested on what appeared to be an old open shaft until it began to fall. Harry reacted to the noise, instantly silently and they all waited, frozen in fear, for any sign that it had been heard. Nothing happened after several seconds and they all relaxed.
"Fool of a Took! Throw yourself in next time and save us all some trouble." Gandalf snapped and Pippin flinched slightly, looking down. "We make for the bridge of Khazad-dûm, quickly." He urged and they fled the room, Legolas and Aragorn pulling Gimli to his feet to run. They moved as quickly as they could considering the hobbits shorter legs and made it onto a crumbling staircase before the sound of drums began to reverberate through the stone halls. "Run!" They dashed madly down the stairs even as several arrows flew through the air towards them. Legolas quickly returned fire, covering the others even as they reached a break in the stairs that they had to jump. Legolas leapt across easily and Gandalf followed, the elf steading him. Boromir swept a hobbit up under each arm and threw himself across the gap before Aragorn tossed poor Sam after them. He went to help Gimli who pulled away and readied himself to jump.
"No one tosses a dwarf." He growled before jumping and he almost made it too except the edge where his foot landed crumpled and he began to fall back only for Boromir to grab him. "Not the beard!" He cried in dismay even as he was pulled to safety. Harry couldn't help chuckling before he nimbly jumped across and then moved to check the hobbits, leaving Aragorn and Frodo on the other section. They were preparing to jump when they all felt it, the slight tremor running through the stairs. The next was stronger and Aragorn waisted no more time, throwing them both across the gap and to the safety of the rest of the company. As they continued to run orcs began spilling out of the darkness even as the temperature began to rise and the tremors increase.
"Gandalf?" Harry called and the other Wizard looked at him, obvious worry in his eyes.
"We must reach the bridge." Was all he said though and Harry nodded, sending out a wave of magic to knock away several of their attackers, clearing more space for them to run. He glanced back and swore as he saw the shadowy flame creeping along the walls behind them.
"Run faster!" Harry yelled and Gandalf too glanced back, fear and determination in his eyes as the bridge came into view.
Legolas ran swiftly across and then moved to fire back at the approaching hoards even as Boromir and Aragorn pushed the hobbits onto the narrow bridge before following them across, Gimli right behind them.
"Get them out." Gandalf demanded and Harry frowned before his eyes widened.
"Do as I say! This foe is beyond any of you." Gandalf gripped his arm tightly. "Keep them safe Hadrian." Then he pushed the younger wizard onto the bridge. Harry stumbled across, knowing what Gandalf had planned. Legolas grabbed Harry as he stumbled near the end of the bridge, helping him onto wider ground and then they looked to find Gandalf standing mid-way across.
"What is it?" Frodo asked nervously as the flames came closer and Legolas gasped in horror as the being was revealed.
"A Balrog." The elf whispered.
"Durin's Bane." Gimli gasped.
"Gandalf!" Frodo screamed when the wizard stood his ground against the approaching danger.
"You cannot pass," he said. The orcs stood still, and a dead silence fell. "I am a servant of the Secret Fire, wielder of the flame of Anor. You cannot pass. The dark fire will not avail you, flame of Udûn. Go back to the Shadow! You cannot pass." Gandalf cried, sword in one hand and staff in the other. Harry stared with wide eyes at the sight, he could feel the power pouring off the older wizard and now he could also see the ring he wore. This was power the likes Tom would have given anything to have and yet Gandalf's magic felt safe and warm even when wielded in an attack. He winced as the whip cracked down but was blocked by a shield of white light. "You shall not pass!" With that Gandalf slammed his staff down on the bridge even as the Balrog stepped out onto it fully. For a second nothing seemed to happen and then the bridge crumpled, sending the Balrog tumbling down into nothing. They all relaxed and Gandalf turned to join them.
"Look out!" Harry screamed as he saw the movement that was too swift for any but Legolas to spot. He instinctively tried to shield the other wizard and cried out, falling back into Legolas' arms at the backlash from the fiery whip even as it tore through his shield to wrap around Gandalf's ankle. The wizard's legs went out from under him and he fell over the edge, barely managing to grab onto the ledge of stone. Harry stared at him, horrified at what was happening and Gandalf stared back.
"Fly you fools." And with that Gandalf the Grey was gone.
So a small change to Moria in that it took longer for them to be attacked but Gandalf needs to become Gandalf the White so he had to fall.