Here I am again with another idea! I think this is my best idea yet, so enjoy!
Once you defeat The Destroyer with full hallowed armor, you will get a message in chat.
"Something is wrong in the dungeon..."
Once you enter the dungeon, you will be attacked by a Time Skeleton, which is like the Dungeon Guardian but is really fast and shoots lazers when you are in the air. When killed it drops "Hax Token" which give +6 Health. It's tool tip is "Either you HAXORED or you are awesome." When you are killed you wont lose anything and will be teleported to some different world. A npc is nearby.
"Welcome to Terrarivale, stranger! All newcomers must see the king. Just go to the castle clad in Silver Brick!" it will say. Once you find the palace, enter it and you will be greeted by a Palace Guard.
"Hello newcomer! Go to the King upstairs." You go to the Throne Room and you see King Red. You talk to him."Hello, terrarian! This is the omly safe haven from the corruption, so make your stay as you please!" He throws out an King's Promise. "Use this to defend yourself from thugs. I promise you won't die with this." It is an katana in the shape of Muramasa. It has the samestats except it is a little slower. It's tooltip is "Something feels strange about this.." When you go outside you will find the corpse of an Palace Guard. Then you will be attacked by a Thug. He has 200 health and does 30 attack damage. He can only be damaged by the King's Promise and other weapons found in this world. After you kill him 3 Palace Guards will rush towards you. They all will say
"You have skill with that sword.. You should go to the Great Blockade, to the east." On the way to the Great Blockade you can visit the Mage Tower, a building that the mage can teleport you back. The wizard then gains the "Time Warp" abillity, making you go back to the area. Once you reach the Great Blockade a guard tells you that they are being assaulted by King Blue's army. You go through the Great Blockade (a huge red brick tower) by pulling a lever. You see a bunch of "Blue's Soilders" They have 100 health, stick out their spears and deal 40 damage and when touched do 20 damage. There are 50 of them, so it will take a while to kill them. But you have guards helping you. They are exactly like Blue's Soilders but when touched do no damage and there are only 20 of them. You can only damage the soilders with the King's Promise. Once they all die a Catapult will appear, with 2000 health. It flings stones towards the Great Blockade, breaking some of it's parts. If the blockade is hit 10 times it will be destroyed. The catapult can be damaged with weapons from other time periods. Once you destroy it, 10 Superb Guards will appear. They are not damaged by any of your weapons and just kill the remaining soilders. Then after that they will be damagable. They have 300 health, when touched do 30 damage and swing Gold Broadswords dealing 30 damage. The last one will drop "Torn Letter" It's tooltip is "To the king of this kingdom." You deliver it to the king and he gives you a Guard's Crossbow. It has the same stats as the Demon Bow but fires faster. With any arrow you can damage someone from this world. After that the king will direct you to the West Blockade. Once you get there you find it's already been destroyed by 3 Superb Guards, 1 Catapult and 1 Blue Champion. Blue Champions have 500 health and do no damage when touched. But they have a King's Promise like you that deals 80 damage. The catapults pelt rocks at you instead of at the blockade. Each one does 10 damage. After you defeat the attackers a Guard will rush towards you. "The Blue King has killed Red! You have to stop him! He is in the Blacksmith right now repairing his sword. Defeat him while he is weaponless!" You visit the Town Blacksmith and are followed by 3 Guards to help you. Once you arrive you will see 2 Superb Guards and 1 Blue Champion. After you beat them the Blue King walks out with a sword strikingly similar to Excalibur. "I've already killed the king. You might as well give up." After that he attacks. He has 5000 health and swings his sword around doing 70 damage. Sometimes he jumps on buildings and shoots Unholy Arrows from a Silver Bow. Each arrow does 60 damage. After you attack him on the roof he jumps off and starts running away to jump on the next building. Once he reaches 1000 health he can only be damaged by the King's Promise. When he reaches 1 Health he will swing his sword really hard, sending a shockwave out. Swing your King's Promise to clash with it and the Blue King will die. After that, your King's Promise disappears. The Blue King drops a "Half Corrupted Blade" It has the same stats as Muramasa except it does a little more damage. It's tooltip is "The blood of the king's brother corrupted the blade. It looks similar to Muramasa.." After that half the town is ruined. You can rebuild it and the NPC's will come back, but all the Guards are dead. The mage survived though. The only NPC that doesn't come back is the Blacksmith (killed by the Blue King)