Pokémon Brilliant Diamond and Shining Pearl feature 493 Pokémon, and some are involved in peculiar ways. While most evolve simply by leveling up, some require held items. One held item you will need if you plan to complete your Pokédex is the Magmarizer.
To get the Magmarizer in Pokémon Brilliant Diamond and Shining Pearl, you will need to encounter a Magby. Unfortunately for those who own Pokemon Brilliant Diamond, Magby is exclusive to Shining Pearl. Players can find this Pokémon in the Grand Underground in the Volcanic Cave, Sandsear Cave, or Typhlo Cavern. Magby has a five percent chance to be carrying a Magmarizer.
To get the Magmarizer from Magby, you can either catch it and take it from it manually or use a move to steal the item. Both Thief and Covet will steal the item as long as the Pokémon using the move aren't holding an item. Pokémon that have the Compound Eyes ability increase the odds of Magby carrying a Magmarizer.
A Magmar holding a Magmarizer will evolve into Magmortar. This is the only way to acquire this Pokémon, so you will need to get your hands on this held item to complete your Pokédex.
For more information on Pokémon, check out Where to find the Razor Claw in Pokémon Brilliant Diamond and Shining Pearl and Where to find the Razor Fang in Pokémon Brilliant Diamond and Shining Pearl on Pro Game Guides.