They seem like the same exact Pokemon except for 2 things:
Gogoat has a higher BST
Sawsbuck is Grass-Normal, where Gogoat is pure grass
Sawsbuck changes within different seasons. It also has a higher speed stat then gogoat. Gogoat does have a higher base stat though. Both Pokemon can learn grass, normal, electric, and fighting type moves but gogoat can learn surf with the HM.
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