My Minecraft mob grinder isn't working. It has a 20x20 spawning chamber, 20 blocks above the ground. I made sure it has no light. What should I do? - Quora
Custom Mob Spawner Mod (1.12.2, 1.10.2) - Control How Mobs Can Spawn - 9Minecraft.Net
Minecraft online mob spawner and /summon command generator
Summon Mob Generator (Java Edition 1.12)
How do I make custom spawners? : r/MinecraftCommands