To get a free legendary Pokémon in Pokémon Scarlet, you have several options:

1. **Indigo Disk DLC Method**
– Complete the main storyline of Pokémon Scarlet to unlock the Indigo Disk DLC.
– Go to the main entrance of Blueberry Academy.
– On the right side of the entrance, you’ll find Nawor, an NPC in a suit.
– Finish 130 solo quests and 12 group quests. Each time you complete 10 solo or group quests, Nawor will give you a snack.
– Use the snacks to decode the locations of the legendary Pokémon. Each snack will reveal the location of a specific legendary Pokémon.
– Go to the decoded locations, and the legendary Pokémon will appear. You don’t need to do anything special; they will be there when you have the key item on you.

2. **Mystery Gift Codes**
– Look for active mystery gift codes that offer free legendary Pokémon.
– For Darkrai, use the code NEWM00N1SC0M1NG by December 21, 2023.
– For Shiny Lucario, use the code SH1NYBUDDY by January 3, 2024.

3. **Trading with 24/7 Streamer Trade Bots**
– Participate in 24/7 trading channels.
– These channels often have legendary Pokémon and shiny eggs available for trade. The availability of specific Pokémon can change weekly.

By following these methods, you can obtain free legendary Pokémon in Pokémon Scarlet.