During the VG Day 1 2023 Pokémon World Championships stream, a passcode to receive Eduardo Cunha's Gastrodon in Pokémon Scarlet and Violet was revealed. The code is: 23WCSGASTR0D0N. The code can be used from August 11th, 2023 until August 14th, 2023 at 23:59 UTC.

Eduardo Cunha's Gastrodon Details:

OT: Eduardo
ID: 230811
Level: 50
Ability: Storm Drain
Tera Type: Water
Held Item: Leftovers
Moves: Earth Power, Icy Wind, Yawn, Protect

Source: https://www.youtube.com/watch?v=SL9DwzrqJz8