Bigfoot is a CJ mission.
Carl has to hunt Bigfoot in Back O' Beyond with several cars and weapons at his desposal.
 Finding Bigfoot
After arriving at the mission location in Shady Cabin, Back O' Beyond, Carl is instructed to kill the legendary creature Bigfoot. He has 20 minutes to locate Bigfoot, who is seen roaming the forest in a short video. Starting from the cabin, Carl can use either a Quadbike or Buggy to start hunting.
After the 20 minutes, if Carl hasn't found Bigfoot, the mission does not end. A Vagos symbol representing him is shown on the mini-map revealing Bigfoot's location. After geting close to him, a video is shown of the area, with Bigfoot visible. He is seen running off.
 Boss Battle: Bigfoot
Bigfoot runs away from Carl and a health bar appears, representing his health. Bigfoot has a lot of health and starts walking towards CJ when he open fires on Bigfoot. His main weaknessess are shotguns. After defeating Bigfoot 4 times, Carl goes up against the Yeti, who is located on Mt. Chillad.
 External Links
Related Threadsthe bigfoot mission mod - last post by @ Sep 23, 2007
I know Bigfoot is fake but listen... - last post @ Mar 16, 2017
seeking bigfoot (version 2) (unlock secret level) - last post by @ Sep 10, 2008
Make up your Own Missions Thread - last post by @ Nov 11, 2008
Bigfoot? - last post by @ Sep 20, 2013