A first-generation Pokémon, one of the strongest ghost types in the series, and an overall iconic Pokémon, Gengar is a powerful teammate for even the pickiest trainers.
How to get a free Gengar in Pokémon Scarlet and Violet
Step 1: Catch a Pincurchin, an electric-type sea urchin Pokémon found on most beaches throughout Paldea. You can even find them on the beach by Levincia, which is where you need to travel for this trade.
Step 2: Once you have a Pincurchin, travel to Levincia. You'll need to find the woman looking to trade her Haunter for a Pincurchin.
Step 3: When you agree to the trade and swap Pokémon, you will receive a Haunter (which is unfortunately nicknamed Hauntikins). As soon as you receive Haunter and the Pokémon is registered in your Pokédex, it will begin to evolve.
Just don't press B and accidentally cancel the evolution!
Let it go through and you'll have a Gengar on your team.