Clefairy is one of the many Pokémon that you will need to find and capture in Pokémon Brilliant Diamond and Brilliant Pearl. You can find it all over the Sinnoh region. Eventually, you'll want to evolve it into its final form, Clefable. But there are some requirements you need to meet. Here's what you need to know about Clefairy's evolution in Clefable into Pokémon Brilliant Diamond and Brilliant Pearl.
There is no need to level Clefariy up to a certain point or increase her friendship. The only thing you need to do is find a moonstone. The only way to find this item is to search the Grand Underground and complete the Fossil Digging minigame. Once Clefairy receives a Moonstone, she immediately evolves.
You will have access to the Grand Underground when you receive the explorer kit. You can get it by talking to the old man who lives near the town's Pokémon Center and gives you the item. From there, you can explore and dig into the walls, looking for fossils and other valuables.
There are multiple evolutionary stones in these walls, but they are rare to spot. The best way to increase your chances of finding them is to find Digletts and Dugtrio in the passages of your Grand Underground cave and increase your bonus on the left side of the screen. It is recommended to reach 35-40 to receive the best results.