In Pokémon GO, players will be able to find and catch Gloom during "Sustainability Week 2022." Every April, Niantic holds the annual event to celebrate the game's popular Grass-type Pokémon such as Venusaur, Cherubi, and Ferroseed. Despite debuting in Pokémon GO in 2016, Gloom has continued to be one of the most sought-after Pokémon in the Mobile title due to its unique evolution into both Vileplume and Bellossom. Because the Generation One Pokémon is normally challenging to find, its appearance during Pokémon GO events like "Sustainability Week" is always welcome news for many players.
The "Sustainability Week 2022" event went live in Pokémon GO on April 20 and runs until April 25 at 8:00 PM Local Time. During the annual celebration, players can find Oddish with boosted spawn rates in the wild. Pokémon GO trainers who travel a lot during the event have a good chance of encountering the Pokémon. Players who use a Mossy Lure Module in Pokémon GO can attract a Gloom using the item at any PokéStop or Gym. The Kanto Poison-type can appear up to 30 minutes after using the Lure during the event.
While Gloom is a featured Pokémon during the "Sustainability Week" event, Pokémon GO players can actually catch the Poison-type year-round. The Kanto Pokémon can be found in specific locations and caught using the right methods. Unlike many other Pokémon, however, Oddish and Gloom are not able to be obtained in the game's current Egg System according to Pokémon GO Wiki. This means that players will only be able to add the Grass-type to their Pokedex using specific methods.
How to Find & Catch Gloom in Pokémon GO
Gloom can be found in the wild in Pokémon Go as it spawns in forests, gardens, and parks. Players looking for the best chance to find the Grass-type or its pre-evolution Oddish can use a Pokémon Go Incense item while exploring grass-based locations near them. Those who don't live near any of those environments can trade Gloom with another player or will need to wait for a future event during a different season. Even outside of Pokémon Go events, players can use the Mossy Lure Module on any nearby Gyms or PokéStops. While Gloom is not guaranteed to show up, the special item attracts Bug and Grass-type Pokémon for 30 minutes. The grass-themed lures can be purchased from the in-game store in Pokémon Go for 200 Poké Coins.
Players who already have Oddish in Pokémon Go can also evolve it into Gloom for 25 Candy. An easy way to obtain candy is equipping Oddish as a buddy and walking around the map. For every three KM traveled, trainers will be rewarded a single candy. The easiest way to catch Oddish, though, is to participate in Pokémon Go events such as April's "Sustainability Week" celebration where the Poison-type has boosted spawn rates. Trainers who missed out shouldn't worry too much as the game will have plenty of upcoming celebrations such as the Pokémon GO Fest 2022 in June which could feature Gloom.
Source: Pokémon GO Wiki