Hello, this is the information I found so far on wild Pokemon holding an item:
General chance: 5%
Exceptions:
Porygon: 33% chance of holding Up-Grade
Porygon: 33% chance of holding Choice Scarf
I'd like to ask, whether the chance of wild Paras or Parasect holding mushrooms is also 5%. Considering the chance of holding a tiny mushroom being 50% in most of the Nintendo games, this seems pretty low...
So does anyone have facts on this? From what I experienced using Thief in Mt. Moon, the 5% seem to be about right :/