Download Soft Mask FREE Unity. 

Soft Mask is a UI component that masks child elements. It works almost like standard Unity’s UI Mask but supports gradients and semi-transparency.

Demo | Documentation | Support Thread

• Easy to use: just drop it on the Game Object in the same way as Unity’s standard Mask.
• Supports Image, RawImage, Sprite, and Texture.
• Works with TextMesh Pro!
• Supports inverted masks.
• Can be easily supported in your shaders.
• Fully real-time: create, destroy, enable, disable, move, rotate and reorder a mask and UI elements at runtime.
• Can restrict input processing to only visible parts of the masked UI.
• Adjustable mask sampling: use black and white images, images with transparency or set the weight of each color channel manually.