Detail this asset from Unity Store: Original Link
This is a paid asset, but now you can download 2D Background Parallax Pack Free.
2D Background Parallax Pack v1.0
2D Background Parallax Pack
Build your game background and parallax effect
With this pack can create a hundred variations and create your unique environment
The texture can be used in old Unity versions.
This pack content:
09 Trees
09 Plants
09 Sun
09 Moon
12 Clouds
02 Star background
09 Flower (more then 24 variations included)
12 Mountain (more then 36 variations included)
09 Mountain background
03 Mountain ready for parallax
02 Ocean waves
05 Paths
05 Sky Background
04 Parallax Examples
The spritesheet are in png format 2048 x 1024 px
*The parallax script included is a third part free-pack
[Free Parallax for Unity (2D)]
https://www.assetstore.unity3d.com/en/#!/content/29422
The see the parallax examples included: https://youtu.be/M3pMMZZuY0E