Region-exclusive Pokémon in Pokémon Go are always difficult to catch. They only occur in a particular area of the world and only become available worldwide during specific events, and those are rare. For example, when trying to catch a Red Striped Basculin, it can only be found in the Eastern Hemisphere. When it becomes available, it's a Pokédex filler. However, can you catch a bright version of a red striped Basculin?
The glossy version of Basculin has not been released and the red and blue striped versions are not available. Basculin was released during the early part of 2020 and we have only seen this Pokémon appear a few times from time to time for world events. Outside of these rare cases, it usually stays in the eastern hemisphere.
We do not know when to expect the release of the brilliant version for Basculin. When it does, we know that both versions will be available worldwide for a short time and that players will be able to catch these two Pokémon at the same time. The chances of getting a bright version of one are in the 450 probability range, so attempting to catch both bright versions will be extremely difficult, but it is possible. Typically, these events increase the chances of finding Pokémon in the wild.