Big Koopa Troopa

Gargantua Koopa Troopas are sub-species of Koopa Troopa. They are gigantic versions of their normal counterparts around the Mushroom Kingdom. The reason for their large size is unknown.

Super Mario Bros. 3
Gargantua Koopas appear in Super Mario Bros. 3 and reside only on Big Island (along with other gigantic creatures like Grand Goombas and Piranhaci Gigantici). Mario and Luigi have a harder time avoiding these Koopas because of their increased size. Despite this, if the plumbers stomp on a Gargantua Koopa, it will hide inside its Giant Green or Red Shell, just like an average-sized Koopa does when it feels threatened. Once inside, the plumbers can kick their shells away. Gargantua Koopa Troopas were members of Bowser's army during his attack on the eight major lands of the Mushroom World. Also their subspecies, Colossal Koopa Paratroopas appeared alongside them as well.

Super Mario World 2: Yoshi's Island
In Super Mario World 2: Yoshi's Island, a regular Koopa Troopa named Hookbill was transformed by Kamek into a Gargantua Koopa Troopa in order to stop Yoshi from reaching World 5. It acted as the boss of World 4.

Super Mario 64
In Super Mario 64, a single Gargantua Koopa Troopa known as Koopa the Quick appears in the game as a friendly racing rival to Mario. He hails from Tiny-Huge Island (an island filled with both miniature and gigantic enemies) but he is the only Gargantua Koopa Troopa seen in the game.

Paper Mario
In Paper Mario, a greedy and nearsighted Gargantua Koopa Troopa named Kent C. Koopa appears as a boss in the game. He is known as a bully and refuses to let anyone pass by him unless they pay his fee of 100 coins. If anyone refuses his fee he will not let them pass and if they disobey him he will proceed to beat anyone up unmercifully. Mario and his partners had to fight him in order to return to Koopa Village. He also taught the Koopa Bros. how to fight.

Super Mario Galaxy 2
They reappear in Super Mario Galaxy 2 in Supermassive Galaxy. Only three are found patrolling a solitary planetoid where they will attempt to flatten Mario if he gets in their way. They can only be defeated with a Spin Drill attack to their belly.