You can find various Pokémon during your journey in Pokémon Brilliant Diamond and Brilliant Pearl. Many of these Pokémon only appear in specific locations, and they can be a little hard to find if you don't know how to activate these encounters. There are also some Pokémon that only evolve from specific items and methods. Here's what you need to do if you want to evolve your Snorunt into a Froslass in Pokémon Brilliant Diamond and Brilliant Pearl.
Before you do anything else, make sure the Snorunt you catch is a female. If you have a male, she won't be able to evolve into a Froslass. It may be necessary to catch a pair of Snorunts before spotting a female. After you have one, consider working for a Froslass.
After capturing a female Snorunt, the next step is to locate a Dawn Stone. It's an evolutionary item that you can find in several places, but one of the most successful ways to find one is to have a Pokémon with the Collect ability on our team or dig for fossils in the Grand Underground. Both are reliable ways to acquire a Stone of Dawn at any point in the game.
Next, you'll need to use the Dawn Stone on Snorunt and it should immediately evolve into a Froslass.