There are multiple Pokémon that you can find throughout Pokémon Brilliant Diamond and Shining Pearl. Many of them have specific evolution requirements if you want them to reach their final form. There’s a particular requirement you’re going to need to meet if you want to evolve Mantyke into Mantine. Here’s what you need to do to evolve Mantyke into Mantine in Pokémon Brilliant Diamond and Shining Pearl.
The only way Mantyke becomes a Mantine is if you have Remoraid in your party. This is a specific Pokémon that you have to find this Pokémon throughout the Sinnoh region, but you’ll need to catch it using a Good Rod. If you don’t have a Good Rod, it does not spawn while you’re fishing.
Once you have Mantyke and Remoraid in your party, all you have to do is have your Mantyke level up, and it becomes a Mantine. We recommend going using this method to make it easier to find Mantine. You can encounter Mantine in the Grand Underground, but it is a bit hard to locate. Thankfully, Remoraid is pretty easy to catch using a Good Rod, so reaching Mantine won’t take you too much time.