Minecraft wiki entry for Rube_Goldberg_machine, associated text: Some mobs attract or repel certain other mobs. Villagers attract zombies, zombies attract iron golems, cats repel creepers, and skeletons attract dogs. Show off mob pathfinding by making a small maze with a trapped mob at the end. Near the end, make the mob step on a pressure plate, tripwire, or have the mob die. You can have multiple mobs for a race.