Giant Pokémon
Giant Pokémon, while having never played a large part in terms of plot, are nonetheless a recurring theme in the Pokémon anime. There are several episodes that have a plot that revolve around unusually large Pokémon, such to the point that it seems to be a rather common mutation for Pokémon to go through.
Mystery at the Lighthouse
Dragonite
The concept of giant Pokémon roaming the earth was introduced by Bill, who was trying to establish contact with a giant Pokémon whose cry echoed across the ocean. Eventually, it appeared in the fog, and though it could not be seen directly due to the fog its silhouette was clearly that of a giant Dragonite. However, the brief encounter ended when Team Rocket attacked the giant Pokémon and scared it off.
Gary's Krabby
Gary's Krabby is much, much larger than the one Ash recently caught.
Ash's Kingler
When Ash's Krabby evolved into Kingler, it was unusually large for its species.
Island of the Giant Pokémon
Although several gigantic Pokémon such as Blastoise, Charizard, and Moltres appear, they are soon revealed to be colossal robots built for a theme park.
Tentacool & Tentacruel
Tentacruel
Just a few episodes later, this episode showed a Tentacruel large enough to knock down skyscrapers. The powerful Tentacruel even spoke to the characters through Meowth, despite Tentacruel having no psychic powers.
To Master the Onixpected
Bruno's Onix
In this episode, Bruno captured a giant Onix that was three times the regular size due to there being more fertile soil in the area.
The Ancient Puzzle of Pokémopolis
The very next episode, has three giants - Alakazam, Gengar, and Jigglypuff. They are ancient Pokémon with odd markings, which were released from ancient devices that function similar to Poké Balls.
Alakazam
Alakazam was released from an ancient device that acts as a lock. The only way for Alakazam to be released is by having a spoon inserted into the lock.
Gengar
Gengar was released from a device shaped like two balls.
Jigglypuff
Jigglypuff was released from a device shaped as a bell, which it uses later on when it Template:M2.
The Joy of Pokémon
Gyarados
A giant Magikarp appears in this episode of whom a Nurse Joy takes care of. Later in the episode, it evolves into a giant Gyarados.
The Mystery Menace
Bulbasaur
The next Giant Pokémon to show up is a Bulbasaur abandoned in the sewers. In the sewers, it grows and mutates to twice its normal size.
Bound For Trouble
Pidgeot and Rhydon
Two episodes later, Ash and company land on an island that is home to giant Pidgeot and Rhydon. Tracey explained that the weather and nutritional resources on the island may have contributed to it.
Grin to Win!
Sunflora
In Bloomingvale, Cyrus has a 3 time prize winning Sunflora that is over twice as tall as normal.
Fly Me to the Moon
Ash and company were visiting an island that was inhabited by overweight Pidgey, which seemed to be brought on by bad eating habits and a general lack of exercise. However, despite this, the Pidgey were still capable of flying.
Enlighten Up!
Goldeen
A giant Goldeen is seen among many water Pokémon.
Now That's Flower Power!
Drew's Roselia
While Roselia is normally a foot tall; the one Drew has is about the size of a small, human child. When it evolves, its size is back to normal.
Gulpin' it Down
Gulpin
The next appearance of a giant Pokémon is part-way through the Advanced Generation era, where a mysterious invention causes a wild Gulpin and Ash's Treecko to grow to the size of buildings.
Whiscash and Ash
Whiscash
This episode contains a story about a Giant Whiscash.
Who's Flying Now?
Winona's Skarmory
The Gym Leader Winona is a trainer to a larger-than-normal Skarmory.
The Garden of Eatin'
Marcel's Snorlax
In this episode a larger than usual Snorlax appears. It is later captured by Marcel.
Claydol Big and Tall
Claydol
The next Giant Pokémon is a gigantic Claydol. It nearly destroyed a small town and had to be captured inside of its own gigantic Poké Ball.
Eight Ain't Enough
Juan's Whiscash
Juan uses a Whiscash that seems to be the same size as the giant one in Whiscash and Ash.
Caterpie's Big Dilemma
Xander's Butterfree
A boy's Caterpie grows to giant size and goes on a rampage, as do Team Rocket's Pokémon. The Caterpie later evolves to Metapod, then Butterfree. Later, it goes after Team Rocket's giant Dustox.
Steamboat Willies!
Mantine
The captain's Mantine seems to be bigger than normal Mantine with Dawn and Ash both being able to sit on it. The Captain also says that his Mantine is quite big in the dub.
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Anorith Fossil
The most prominently displayed fossil in Byron's collection is a large Claw Fossil. Were it to be revived, the Anorith would be three times larger than normal.
