I honestly think Diligence is the most frightening of all the Fundamentals. There's something so... cynical and haunting about how traditionally good traits of resilience and doing one's duty also being content with one's own position to be enslaved and forced into said duty. You just are. You exist for your task.
The Clockwork is such a good demonstration alongside their "humanoid" form. All machine, all flesh used for a particular design. My favourite Fundamental I think! ♥