Upon reading the previous “Melkor” suggestion made by another user, I started to think that maybe there should be a new game mode dedicated to Dagor Dagorath. It would sort of be an apocalypse style game mode where you spawn in the overworld. For the first few days, it is normal survival Minecraft. But then, after that the next stage happens, where low level Middle-earth mobs start to naturally spawn as well as low level Middle-earth ores and materials. No biomes and no structures. Just the mobs. The stages after that would each spawn increasingly difficult mobs and higher level ores and resources. One of the final stages would include a new biome called Desolation. This Desolation biome would include war related structures for good and evil factions. These structures would be dispersed randomly throughout the Desolation biome, creating the illusion of a ongoing war between good and evil. As the later stages progress. Each Desolation biome would be bigger and include more higher level structures. The fourth to last stage would spawn structures and mobs from the Ice level of the Utumno faction. The third to last stage would spawn structures and mobs from the obsidian level of the Utumno faction. The second to last stage would spawn structures and mobs from the fire level of the Utumno faction. The start of the final stage would make the Desolation biome be so massive that it would be the only biome. The final stage would be broken up into sub stages, with it spawning increasingly difficult bosses in each sub stage. The final sub stage of the final stage would spawn Melkor as an intensely difficult boss fight.
I forget to mention that before the low level stages, there would be a quest line of finding the Silmarils. The first would be found in a new structure in the deep ocean called Ulmo’s sea palace, the second would be found in another new structure in the Nether Basalt Delta. After that, there would be a new quest line to get to Valinor. To do so, you must get a new item crafted by combining the Dragon Egg with eight blocks of undying, which in turn is crafted with nine totem of undying. After that, you would get the Undying Dragon Egg, which you would combine with beacons of undying, which in turn is crafted from eight blocks of undying surrounding a beacon.
After that you would build a portal frame with the beacons of undying and use the Undying Dragon Egg on it like flint and steel.
After you arrive in Valinor, you would do multiple quests to gain the trust of the Vanyar, Maiar, and Valar. Once you do this, you would be able to get access to a new dimension where you would arrive at the Door of Night and speak to Eärendil, somehow obtaining his silmaril.
With all of the Silmarils in your possession, and potentially Feanor released from the Halls of Mandos, you would travel back to Valinor, witness it’s destruction and flee to the overworld, where the first stage would begin.