Can you identify this minifigure with green skin and red hat? I would like to know who this minifigure is or what set it belongs to.
The minifigure that you have is Kithaba from Star Wars: 

https://www.bricklink.com/v2/catalog/catalogitem.page?M=sw397#T=P

it appears in this set:

9496-1: Desert Skiff