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All Grass Type Pokemon are passively buffed/nerfed by all Weather.
>Sun
Raises Speed of the Pokemon by 1. Stacks with Chlorophyll.
>Rain
Now restores 1/10th of Pokemon's HP at the end of the turn. Stacks with Rain Dish.
>Sand and Hail
Pokemon now takes 1/10th damage at the end of each turn instead of the normal 1/16th