Board Thread:Game Help/@comment-27571063-20160408124942/@comment-26993120-20160509040138

If the Corruption is within 50 blocks of a house, NPCS won't move in. That's why it's usually easier to make an aboveground Mushroom biome. All you need is some mud blocks and only one thing of mushroom grass seeds, minimum. Make it float above the ground in a Hallowed biome so it doesn't get Hallowed/Corrupted; NPCS will live near Hallow biomes. Hope this helps!