If you're building a design system and need to nail down how illustrations should look and work across your product, this gives you the full framework. It walks through the key visual decisions like geometric versus organic, flat versus dimensional, and how detailed to go. You'll define color rules, character design if needed, and spell out the different illustration types from spot illustrations to error states. What I like is that it doesn't just focus on the art style itself but also covers the practical stuff like when to actually use illustrations, how they fit your grid, and accessibility considerations. It's basically the template for turning "we need consistent illustrations" into an actual documented system your team can follow.
npx skills add https://github.com/owl-listener/designer-skills --skill illustration-style