This teaches you the actual theory behind squash and stretch animation, not just the surface mechanics. You get volume preservation rules, the elasticity spectrum for different materials, and specific percentages to start with (10% for energetic motion, 2-3% for subtle work). What I like is it connects the principle to real implementation across UI buttons, character rigs, and game feel, with concrete numbers like 95-98% height for button presses. The interaction with timing and follow-through is well explained. It's focused on making you understand why the deformation amounts matter for different contexts rather than just giving you easing curves.
npx skills add https://github.com/dylantarre/animation-principles --skill squash-stretch-mastery