This isn't really in Minecraft; It is just fan-fiction.
This is the story of Minelantis and how it came to be underwater. It takes place a few years before Herobrine.
It was a dark night. There was an army of Zombies, Creepers, Endermen, Spiders and Skeletons, hidden in the forest, amassed by one Ghast. This Ghast was the leader. His name was Ghustias, and he had been one of just five of his species left before they fled to the Nether. They had been pushed to the brink of extinction by humans, and now he wanted- no, he needed his revenge.
They had just destroyed a small village and killed most of the humans, though some of their own had fallen. They were planning next to go to the large city of Minelantis, which was on an island and was teeming with people. Those people had good weapons, but the monster’s numbers were far greater, plus the Skeletons had their bows, the Endermen could teleport and the Spiders had their venom.
As Ghustias told his plan to his most trusted leaders- one of each species- he heard a twig snap, and a tiny whimper. Hmmm... He thought. It must just be one of the younger creepers. I have to tell... But just then, his Spider leader sniffed the air, and hissed. “A HUMAN!!!” He whispered. “How did it find us?!” “Shhhhh!” Ghustias shushed him. He floated to the edge of the forest...
There was nothing there.
“Must have been your imagination,” he said to the Spider when he came back.
“But it wasn’t! I know a human when I smell one!”
“Be quiet!” said Ghustias. He then continued telling them his plan.
Now, the thing they heard in the woods actually WAS a human. It was a young boy from a nearby village. He had strayed into the forest and come upon the leaders talking. He now rushed home to tell his father. At first, he didn’t believe it, but his son brought him to the clearing and he saw the monsters. Then the father immediately rushed to his house, grabbed his only Gold Sword, and set out for Minelantis, to warn the people.
A FEW HOURS LATER
Ghustias was enraged. They had been counting on the element of surprise, but somehow the humans had found out! They were lined up outside the walls with bows, swords, and armor. Archers were atop the wall. The monsters couldn’t make it past without several of their own falling.
He held council with the leaders. They finally decided creepers would go first, to blow some of them up, then zombies, to turn some of the humans to zombies, then spiders, to poison the remaining and climb the walls, then lowering strings for the rest of the army to climb. Skeletons would stay back and shoot the enemy with their bows. Lastly, Endermen would come and finish off any humans that were left.
With this plan, they marched towards the city.Ghustias was still steaming with anger. One of the monsters must’ve betrayed them. Probably one of those pesky Enderman... Oh well. The battle had started. Arrows flew from both sides. “CHARGE!!!” screamed Ghustias.
The creepers charged. The humans retreated as they blew up. Some humans fled as the zombies approached. Ghustias flew in, blastng the humans with fireballs. It is working! he thought. Suddenly, he felt a searing pain in his left eye. A human had shot him with a bow! He let out a terrifying screech of pain and anger. He was more furious at the humans than ever. All thoughts of slightest mercy was gone in an instant. “Bring in every charged creeper we have!” He screamed, turning to the leader of the Creepers.
“But, sir, if we do, it could blast the city-”
“I DON”T CARE!!!” roared Ghustias. “BRING! THEM! IN!”
The creeper leader whistled, and scores of glowing blue creepers streamed out of the woods. At the sight, every human and monster fled... except Ghustias. He had to watch. Sssssssss... came the sound, like music to his ears. Then, like a nuke, there was a gigantic explosion.
Ghustias was thrown backward as a huge flash lit up the night and an extremely loud KA-BOOM! made villagers for miles around cover their ears. He rammed into a huge oak that was waving like a sapling. His weight made it snap off and land yards away. He opened his good eye and groaned. The explosion had made him almost deaf, and the branches of the tree had scratched him.
There was still a mushroom cloud in the air, but the city was... gone! Unsteadily, Ghustias rose into the air and looked around. There were people swimming in the water and lots of rising bubbles, but no city!
Then Ghustias realized: the city had sunk!
THAT was what the Creeper leader had been telling him! The explosion had destroyed the land connecting Minelantis to the shore, and that combined with the force of the explosion had sunk the island.
At first Ghustias was shocked. Then he laughed. All the humans would drown! He had conquered Minelantis!
At least, that was what he thought. After the city came to rest at the bottom of the sea, the Mer-People moved in. Unfortunately for Ghustias, humans drove him into the Nether a few weeks later, and he stayed in a fortress, still angry at the humans, for the rest of his life.