Gloom debuted in Pokémon Scent-sation!, under the ownership of Erika. Ash first rescued it from the Celadon Gym when it was set on fire due to Team Rocket's actions. Erika first met Gloom when it saved her from a Grimer when she was a girl. According to this episode, Gloom is a very useful Pokémon, as Erika uses Gloom's stench as a recipe for creating perfume. It reappeared in flashbacks in Pikachu's Goodbye and the Japanese version of Gotta Catch Ya Later!.
In Make Room for Gloom, Florinda initially wanted to evolve her Gloom into a Vileplume. However, Florinda eventually decided it didn't need to evolve after it beat Team Rocket with its powerful Solar Beam attack. It reappeared in a flashback in Bulbasaur... the Ambassador!.
In Pokémon Food Fight!, Gulzar owns a Gloom. Ash tried to battle it with Charizard, but he sent Squirtle and then Snorlax out by mistake, which resulted in Snorlax trying to eat Gloom's leaves.
In Whichever Way the Wind Blows, multiple Gloom either evolved into Bellossom or Vileplume depending on the direction of the wind which contained fragments of Sun Stones and Leaf Stones.
In Bucking the Treasure Trend!, multiple Gloom attacked Ash, his friends, and Buck as they searched for Dandelion Island's treasure.
In A Fork in the Road! A Parting of the Ways!, a Gloom caused Jessie and Wobbuffet to fall off a cliff.
In Pokémon Scent-sation!, a Gloom was in the Celadon Gym, separate from the one Erika bonded with as a child and then kept as one of her battling Pokémon.
In Showdown at the Po-ké Corral, multiple Gloom were living at Professor Oak's Laboratory.
In Pikachu's Vacation, a Gloom was at the Pokémon Theme Park.
In Round One - Begin!, a Trainer's Gloom competed in the Indigo Plateau Conference.
In Friends to the End, a Trainer's Gloom was at the closing ceremonies of the Indigo Plateau Conference.
In The Power of One, a Gloom sensed the disturbance caused by Lawrence III.
A wild Gloom appeared in Pikachu's Rescue Adventure.
Multiple Gloom appeared in Foul Weather Friends.
In The Fortune Hunters, a Gloom was stolen by Butch and Cassidy.
In Ariados, Amigos, a Trainer's Gloom was at the Pokémon Jujitsu Academy.
Two Gloom appeared in The Grass Route, with one being wild and the other under the ownership of a Trainer competing in the Grass Tournament.
In Delibird's Dilemma, multiple Gloom helped Bulbasaur find some Christmas presents dropped by a Delibird.
In Bulbasaur... the Ambassador!, multiple Gloom were among the feuding Pokémon at Professor Oak's Laboratory.
In Johto Photo Finish, a Gloom was fed by Tracey at Professor Oak's Laboratory.
In Grass Hysteria!, multiple Gloom were residents of the Forbidden Forest.
In Hokey Poké Balls!, a Gloom was at Professor Oak's Laboratory.
A Gloom appeared in Destiny Deoxys.
A Coordinator's Gloom appeared in Harley Rides Again.
In Pinch Healing!, a Gloom was a resident of Fennel Valley.
In Once More With Reeling!, a Coordinator's Gloom participated in the Terracotta Contest.
In The Grass-Type Is Always Greener!, a Gloom was found by Cheryl's Mothim while searching for the Enchanted Honey. Gardenia tried to catch it, but it managed to run away.
A wild Gloom appeared in Pokémon Ranger and the Kidnapped Riolu! Part 1 and Part 2.
In the opening sequence of Arceus and the Jewel of Life, a Gloom was in an Aroma Lady's field of flowers.
A Gloom appeared in League Unleashed!, under the ownership of a girl.
In Under the Pledging Tree!, a Trainer's Gloom was present during the Coumarine City Festival.
A Gloom appeared as an image in A Performance Pop Quiz!.
A Gloom appeared in I Choose You!.
In Alola, Kanto!, three Gloom and a Vileplume got into a fight with a Weepinbell and Victreebel, which Bulbasaur had to break up.
Three Gloom appeared in a flashback in Enter Pikachu!.
A Gloom appeared in Legend? Go! Friends? Go!.
A Trainer's Gloom appeared in Trade, Borrow, and Steal!.
A Trainer's Gloom appeared in To Train, or Not to Train!.
A Trainer's Gloom appeared in JN057.
||Gloom, the Weed Pokémon. Gloom gives off a very unpleasant smell. While strong against Water-type Pokémon, Gloom is weak against Fire and Flying types.
||Gloom, the Weed Pokémon. It gives off a powerful aroma that can cause those to smell it to faint from two miles away.
Ash & Pikachu
A Gloom appeared in Do Your Best Bulbasaur!!, where it was seen at Professor Oak's Laboratory.
The Electric Tale of Pikachu
In Days of Gloom and Glory, Florinda Showers was shown to have multiple Gloom, unlike her anime counterpart. They were used to make herbal medicines.
Pocket Monsters HGSS
A Gloom appeared in PMHGSS14.
Pocket Monsters HGSS Jō's Big Adventure
A Gloom appeared in JBA4, under the ownership of Ariana.
Gloom first appeared in Paras Sight, under the ownership of Erika. It was part of her Gym team, but it wasn't shown battling.
A Gloom appeared in The Last Battle XIII as one of the Pokémon sent to participate in the fight in Ilex Forest.
In Softening Up Kakuna, a Gloom was used by a Trainer that was challenging the Battle Factory.
A Gloom appeared in Out-Odding Oddish, under the ownership of a Pokéathlon participant.
Team Rocket Executive Ariana's Gloom appeared in Pleased as Punch With Parasect.
Pokémon Battle Frontier
A Gloom appeared in Final Battle: Versus The Salon Maiden.
Pokémon Gotta Catch 'Em All
A Gloom appeared in The Raining Crystal Ball.
A Gloom appeared in GDZ23.
Shu caught a Gloom, as seen in GDZ64.
A Gloom appeared in GDZ67, under the ownership of a monk.
Pokémon Pocket Monsters
A Gloom appeared in Big Struggle with the Powerful Opponent Venusaur!!.
A Gloom appeared in Aim to be the No. 1 Pokémon!, under the ownership of Erika. It evolved from an Oddish and then into a Vileplume as part of an act.
A Gloom appeared in Demanding Tests at the Pokémon School!.
A Gloom appeared in PZ05, under the ownership of a Gym Trainer at Celadon Gym.