Gargantua Koopa Troopas are oversized sub-species of Koopa Troopas that roam around the Mushroom Kingdom. They have the same general behaviors as a regular-sized Koopa Troopa but their larger size makes them harder to avoid, they commonly require different tactics to defeat but in some cases, can be defeated in the same ways as a regular Koopa Troopa. Like the regular-sized Koopa Troopas, Green Gargantua Koopa Troopas tend to walk off edges while the Red Giant Koopa Troopas turn back at edges. A Gargantua Koopa Troopa's Shell is large enough and can also be used to shred through clusters of Brick Blocks. They hail from Giant Land and the Supermassive Galaxy.
Gargantua Koopas first appear in Super Mario Bros. 3 where they can be found exclusively in Big Island. Aside from them, Grand Goombas, Colossal Paratroopas, and Piranhaci Gigantici also appear, they all reside on Big Island trying to attack Mario or Luigi. Like normal Koopas, they hide in their shells when jumped on and can be kicked around too. Despite it's larger size, a Gargantua Koopa Troopa isn't any more durable than a basic Koopa Troopa and can be defeated in the same ways, with the effects of a Fire Flower, Super Leaf, Tanooki Suit, Hammer Suit, or a Starman.
A single Gargantua Koopa Troopa named Hookbill the Koopa appears in Super Mario World 2: Yoshi's Island alongside Yoshi's Island: Super Mario Advance 3. Hookbill the Koopa was a regular Koopa Troopa that was turned into a Gargantua Koopa Troopa by Kamek's magic. Hookbill the Koopa acts as the boss of World 4 and can be defeated by tossing eggs at his face and ground pounding him.
A single Gargantua Koopa Troopa named Koopa the Quick appears in Super Mario 64 and Super Mario 64 DS. He is raced on both Bob-omb Battlefield and Tiny-Huge Island, winning the race will reward Mario with a Power Star, in Super Mario 64 DS, Koopa the Quick will only accept a race with Mario and won't race with anyone else however it is possible to race Koopa the Quick as anyone else by wearing a Mario Cap.
A Gargantua Koopa Troopa named Kent C. Koopa appears as a boss in Paper Mario, he is seen as a big bully who refuses to let anyone pass unless they pay him 100 Coins, if they refuse to pay up, he won't let them pass and if they disobey, he will beat them up without any mercy. Mario and his team need to fight him to return to Koopa Village, Kent C. Koopa is also notable for being the master of the Koopa Bros.
After many years of absence, Gargantua Koopa Troopas reappear in Super Mario Galaxy 2 as enemies found in Supermassive Galaxy. These enemies are only in three on a small planetoid in the galaxy. They can only be defeated by being drilled from underneath their bellies with the Spin Drill. Gargantua Koopa Troopas can also be stomped on endlessly to rack up infinite 1-Ups.
Gargantua Koopa Troopas also appear in New Super Mario Bros. U as well as New Super Luigi U and New Super Mario Bros. U Deluxe. They are very rare, and only appear in the level Jungle of the Giants. They behave similarly to regular-sized Koopa Troopas except they walk slower and they have a slightly different dance. A Gargantua Koopa Troopa can be forced in it's shell by stomping on it and then kicked around, the Gargantua Koopa Troopa's shell is also strong enough to shred through masses of Brick Blocks without ricochetting. Unlike Super Mario Bros. 3, carrying their Shells is now impossible. Gargantua Koopa Troopas can be defeated with ground pounds or the effects of a Fire Flower or Starman, the effects of an Ice Flower or Penguin Suit can freeze them but they break free instantly due to their size.
This is the first game where the Gargantua Koopa Troopa as a species is bipedal and wears shoes.
Gargantua Koopa Troopas reappear in Super Mario Maker as well as it's two sequels. In these games, a Gargantua Koopa Troopa can be made by dragging a Super Mushroom to a Koopa Troopa. They act the same like in New Super Mario Bros. U, in all themes and can be defeated with ground pounds or the effects of a Fire Flower or Starman. A Gargantua Koopa Troopa can also be given wings to become a Colossal Paratroopa.
Gargantua Koopa Troopas reappear in the remake of Mario & Luigi: Superstar Saga, Mario & Luigi: Superstar Saga + Bowser's Minions replacing the Ankoopas found throughout the game. They have the same dialogue and purpose as the Ankoopas from the original game. They block various paths which lead to latter areas of the game and can be knock over once the Fire Tickle is mastered.
Giant Koopa Troopas are bigger variants of the Koopa Troopa. In Super Mario Galaxy 2, they seem to always have an angry look on their faces.