The Wither Invasion — Mark Cheverton

Both Watcher, the young NPC leading the villager army, and Krael, King of the Withers, have taken magical weapons from the ancient Vault of Weapons. Watcher is now able to raise a powerful army using dark magic discovered by the warlocks many centuries ago, but Krael has gained complete control over all the monsters of the Overworld and now possesses a vast army, threatening not only the Far Lands but all of Minecraft.

Both Watcher and Krael have learned that the most powerful weapon of all still lies out of their grasps: the Nexus of Might. Only the warrior that possesses the key to the Nexus will be able to stop their enemy. When Krael takes the key, Watcher must sacrifice anything and everything to stop the King of the Withers, before the magic of the Nexus destroys the Far Land and the Overworld forever.