If you’re looking to breed Mr. Mime to receive Mime Jr., you’re going to need the Odd Incense. It’s the only item that Mr. Mime accepts so that you can receive an egg with Mime Jr. in it. Here’s what you need to know about where to find the Odd Incense in Pokémon Brilliant Diamond and Shining Pearl.
You’ll need to adventure through the game and make your way over to the Solacein Ruins. You can find it to the east of Solacein town, where you can find the Pokémon Nursery. To reach the ruins entrance, go to the east in the city, where you’ll have to hop down multiple rock cliffs and stay to the right side as much as possible. The entrance to the Solacein Ruins will be to the far east.
You’ll need to delve into the ruins and continue going down as much as you can. Make sure to check every room you explore and interact with the rocks in the center of these rooms. Some of these rocks contain items. You’ll also have the chance to encounter Unown while you’re down here.
The room you’re looking for contains four Poké Balls inside it. The one on the right side, in the back, will be the Odd Incense. You can then give this to your Mr. Mime so you can breed Mime Jr.