Giant Pokémon are Pokémon which are significantly and abnormally larger than the normal size specifications. There have been several occurrences of giant Pokémon in the anime.
Examples of Giant Pokémon
In the episode Mystery At The Lighthouse, a giant Dragonite appears towards the end of the episode, where Bill is searching for it. In the same episode it is revealed that Gary Oak managed to capture giant Krabby.
In the episode Island of the Giant Pokémon!, some giant Pokémon can be seen such as Pikachu, Blastoise, Venusaur, etc., although at the end of episode it is revealed that they were mechanical replicas of a theme park.
Several giant Onix appeared in To Master the Onixpected. One of them, which had scar-like markings on the right side of its head, was in extreme pain due to wild Sandslash getting stuck between its boulders. The pain was so strong that it caused the giant Onix to rampage wildly while screaming in pain all along. After Bruno removed Sandslash, the giant Onix was very thankful for relieving its pain and allowed itself to be caught by Bruno. At the end of the episode several giant Onix surrounded Team Rocket and glared at them with anger.
In the episode The Lost Lapras, when Ash and Misty tried to stop three thugs from attacking Lapras, they got angry and sent out their Pokémon to attack them. One of the thugs had Spearow which was bigger than usual.
An oversized Bulbasaur appeared in episode Mystery Menace. After its former trainer abandoned it in the sewers, it spent many years there without evolving or gaining experience, which caused it to grow twice the normal size.