Dream Radar is a spin-off game for the Nintendo 3DS that allows you to collect Pokémon by exploring dreamscapes and catching them using your Pokédex. While you can find rare and powerful Pokémon in Dream Radar, legendary Pokémon are not available in this game.
To encounter and catch legendary Pokémon, you'll need to play the main series Pokémon games such as:
* Pokémon Black and White
* Pokémon Black 2 and White 2
* Pokémon X and Y
* Pokémon Omega Ruby and Alpha Sapphire
* Pokémon Sun and Moon
* Pokémon Ultra Sun and Ultra Moon
* Pokémon Sword and Shield
* Pokémon Brilliant Diamond and Shining Pearl
* Pokémon Legends: Arceus
* Pokémon Scarlet and Violet
You can also find legendary Pokémon in Pokémon GO and Pokémon Masters EX mobile games.
Remember that the availability and methods for catching legendary Pokémon vary depending on the game you're playing. Be sure to consult the game's guides or online resources for specific information.