Scream Tail is one of the many new Paradox Pokémon that you can get in Pokémon Scarlet and Violet. Scream Tail looks like an abnormal Jigglypuff and is exclusive to Pokémon Scarlet. The Pokemon can only be found in one location in all of Paldea, and unfortunately it can’t be reached until you’ve completed most of the game. Scream Tail is also considered a Legendary or Legendary Pokemon, making it more of a challenge to take on.
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How to catch Scream Tail in Pokémon Scarlet and Violet
All of the Paradox Pokémon are in Area Zero, the crater in the center of Paldea. You will not gain access to Area Zero until you complete the Path of Legends, Victory Road, and Starfall Street quests. Once you complete Path of Legends, Professor Sada or Turo will ask you to come to Area Zero with their son Arven. You must reach Victory Road and Starfall Street for Nemona and Penny, respectively, to join your party. When all four of you are ready to go to Area Zero, the Zero Gate will be marked on your map. From the entrance of the gate you can fly to Area Zero with Koraidon or Miraidon.
When you first arrive in Area Zero, the professor will direct you to reactivate the four research centers in the crater. When you get to the second research center in Pokémon Scarlet, you’ll come across a Scream Tail. Penny would mistake it for a normal Jigglypuff, but then she gets scared and fights it with you. You can’t catch the Scream Tail you’re fighting with Penny, but after that, the Paradox Pokémon will start spawning in the lower parts of Area Zero. The Pokémon is particularly numerous in the caves in the lowest parts of Area Zero, where Research Center 4 and Lab Zero are located.
Scream Tail is a Fairy- and Psychic-type Pokémon and is weak to Poison, Ghost, and Steel-type moves. However, since Poison is weak to Psychic-type moves, it’s best to avoid Poison-type Pokemon against Scream Tail and instead focus on Pokemon that can use Poison-, Ghost-, or Steel-type moves.
https://www.gamepur.com/guides/where-to-find-scream-tail-in-pokemon-scarlet-and-violet Where to find Scream Tail in Pokemon Scarlet and Violet?