GSAP always had the tried-and-true "bounce" ease, but there was no way to customize how "bouncy" it was, nor could you get a synchronized squash and stretch effect during the bounce because: The "bounce" ease needs to stick to the ground momentarily at the point of the bounce while the squashing occurs. Bounce.easeOut offers no such customization. There was no way to create the corresponding [synchronized] scaleX/scaleY ease for the squashing/stretching. CustomEase solves this now,