Randomly spawing in all the places thar normal berrie bushes spawnd, there could also spawn poison berrie bushes. These would be like all other berrie bushes except for the slightly different texture on the berries, and that when eaten will give negative effects, probably posien and hunger. (Although mabye they'd also or instead give nausea, slowness, blindness, weakness, wither, or mining fatigue).
The purpose of this would to be add a bit more of a forage, or survival-type feel to the mod by giving players reason to make sure berries are not poisenous before they eat them.
Alternatively, magic berries could be added that give positive effects or have some brewing function. However, I know that these are not canon and that I can not expect them to added.