Minecraft wiki entry for Achievement_guide, associated text: Find a hostile mob. In the Overworld, they can only spawn in darkness, so you should wait until night, or find a dark area like a cave. In the Nether, most can spawn in bright areas. In the End, endermen can only spawn in darkness. You can also find a spawner in a dungeon, mineshaft, stronghold, nether fortress, or woodland mansion and wait for a monster to spawn. Silverfish can be hidden in stone blocks in mountains biomes, and will spawn when the stone is broken.