When I looked at the Shulk one of his abilities is the ability to break stone with there fists but when I tried it out I notticed some issues. But to explain in clarity as a refresher the Shulk can mine Stone with similar power and speed to a stone pickaxe and this speed can not be impeded by any effect or condition of the environment. The first problem is this ability to break stone does not apply to cobblestone while not a bug in itself it is in my eyes invalid since cobble like the other stone variants are of the same material and you would expect the Shulk to just as easily punch through it not have a harder time with it as the pickaxes tend to show.

As for my Enhancement suggestion part I believe the Shulk should be able to mine Coal, and Iron because the power of the punch is similar to that of a Stone pick which can mine those 2 in particular. It also would not be a bad idea to look into other materials that a stone Pickaxe can mine to see what else slipped through the cracks.