In this short tutorial, we’ll show you how to unlock or get Skull Fossil Pokemon in Pokemon Brilliant Diamond and Shining Pearl.
Fossil Pokemon will be available to unlock after you get ride of the first gym leader. Once you have done that you need to go to the underground man's house through the forest and then talk to him to get the explorer kit. This will unlock the underground. He will also give you a tutorial about that.
After you enter the underground you need to look on your map for yellow spots, you'll notice a yellow diamond. This is where you're going to be digging for different things like a fossil or a statue and stuff like that.
So items that you're searching for are going to be random, so eventually you will find a skull fossil. Once you do, you just need to return to the mining town where you fought the first gym leader and go to the mining museum. Once you enter there just talk to the person behind the counter with blue hair. He's going to turn that fossil into a Pokemon. He's going to be a little bit rude to you and tell you to leave the building so just quickly leave and then re-enter to the building again and that will unlock your Fossil Pokemon.