Clay Mode Advanced is a 3ds Max script that reproduces the clay-style viewport shading found in modeling applications such as ZBrush and Mudbox. It creates a ShaderFX shader with matcap UV on the fly, assigns that material as the viewport override, and turns on Rendering Setting mode. The effect runs as a toggle.
The download includes 30 matcaps, and you can add your own textures to the Matcaps folder. It is compatible with 3ds Max 2018 and higher. The script is based on SuperClayMode v1.1 by Changsoo Eun and edited by Wuan Hyu.
Because it works as a toggle, you set up a button or shortcut through Customize User Interface, where it appears under the csTools category. Running the script while holding SHIFT opens a matcap selection dialog, and the chosen file path is stored so you do not have to reassign it each session.