This mecha paper model is Green Gumdrop Dude (Candy Person 10),a Candy Person who first appeared in the episode "Mystery Train", based on the American animated television series Adventure Time, the papercraft is created by WebDude.
He was one of the people who were thought to be the "murderer" by Finn. Colonel Candy Corn explained that he could have had one enemy on the train, but couldn't finish since he was "killed." This made Finn wonder who this person could have been, and Green Gumdrop Dude said that it could be him, since Finn was saying "it could be anyone." This made Finn believe that the murderer was him, and that he said that so he can get away with the murder. He was "killed" after this happened. He is seen at the end of the episode with cake in his hands, walking with Dr. Donut.
He had no official name until he was mentioned in the "Candy Kingdom Song." He was mentioned as being in-between the Royal Tart Toter and Grape Popsicle Guy. [Source: wikia]
You can download the papercraft template here: Adventure Time - Green Gumdrop Dude (Candy Person 10) Free Papercraft Download