Originally debuting in the game in May 2019, as well as the two forms, each has an evolution to discover, too - Gastrodon.
All of these all of which will help flesh out your Gen 4 Pokédex.
How to get East Sea Shellos and West Sea Shellos - or Pink Shellos and Blue Shellos - in the latest Pokémon Go event
Shellos, described as the "sea slug Pokémon", first appeared with both its West Sea and East Sea forms in May 2019.
You can find both forms of Shellos throughout the duration of the Ultra Unlock 2021: Space event by:
- Completing the 'Make 7 Great Curveball Throws' event research task (random chance of East Sea or West Sea)
- Step 4 in the Ultra Unlock 2021: Space Research quest (both forms when completing the 'Make 7 Great Curveball Throws' and 'Make 7 Nice Curveball Throws in a row' challenges)
- Hatching 7km eggs
- Appearing in Tier 1 Raids
- Spotlight Hour (East Sea on Tuesday 10th, West Sea on Tuesday 17th)
Though Shellos doesn't spawn in the wild, there are thankfully plenty of ways to get your hands on them.
Those completing the Ultra Unlock 2021: Space research quest will see both forms rewarded during the fourth step. However, that's just one of each Shellos type - and chances are you'll want more along the way.
The most unpredictable is 7km eggs - since there is a wider pool of event creatures you can also hatch - as well as the research task, where you have no control over which form you'll receive.
This means Tier 1 raids are preferred - especially as they can be completed solo - though obviously depends them appearing in gyms in your area.
However, it's the two Spotlight Hours which are the best way to get East Sea and West Sea Shellos, with each form having a dedicated focus.
This is by far the easiest time to catch them, as they will be spawning in the wild for an hour over each subsequent week. This is the perfect chance to get plenty of Shellos candy too - you'll ideally want 100 total to evolve each 'pink' and 'blue' Shellos to get the respective colour Gastrodon.
The Season of Heritage continues in 2022, along with the XP Challenge and a refreshed Go Battle League. Ongoing are Arlo, Cliff, Sierra counters and Giovanni counters. The major updates in the previous year include a level cap increase, the introduction of XL Candy, boosts to some XP sources and the addition of Platinum Medals.
In short - by the end of the Ultra Unlock event, you should have had plenty of chances to get both Shellos variants, especially if you can make your way to some raids and catch the Spotlight Hours. Best of luck!