Koopa Troopa is a specific subspecies of Koopa. They are the most common species of Koopa, but are also the weakest and most cowardly of the species. They make up a huge chunk of Bowser's army. The early iterations walked on 4 legs but now they normally walk on two. There are a few variations mainly in shell color as well as a very closely related Paratroopa.
Although its not clear if Shellcreepers are related to Koopa Troopas it is clear that they are indeed part of the Koopa Species family fitting in there somehow as a possibly a evolutionary ancestor of the Koopa Troopa although this is still unconfirmed becasue not all of the Nintendo Game theorist community agrees that Shellcreepers might even be a Koopa even if there unanimus that there not a Koopa Trooper.
As a member of Bowser's army, they try to attack Mario so that one touch can eliminate his power-ups. However, the Koopa troopas are dim-witted and cowardly, quick to hide in their shells or run away and the green shelled variation wander aimlessly. A simple step on them will cause them to hide in their shells. Other times they'll be flipped on their backs or kicked out of their shells.
The red-shelled variation is slightly smarter in that it will never leave the platform it originates from, avoiding to fall down cliffs and kill themselves. This obviously does not include Bowser.
There are also smarter Koopa Troopas. Most of these live in peaceful villages outside of Bowser's rule or lad forces under Bowser. Koopas have been shown to have capability to drive carts, pilot giant robots, play a variety of sports, and run banks.
Super Mario Bros.
Koopa Troopas first appear in Super Mario Bros. as a species Mario or Luigi have to step on in order to make it a shell and kick it. The underground Koopa Troopa is a darker variation of the Green Koopa Troopa.
Super Mario Bros. 2
In this game Koopa Troopas enemies are not found. However there is evidence that Koopa Troopa's had been in this place in the past. This is indicated when Mario sometimes discovers a Red Koopa Troopa Shell item. The Koopa Troopa Shell item is used as a weapon to kill other enemies you find such as the Shy Guys.
Super Mario Bros. 3
Super Mario Land
Instead of normal Koopa Troopas, there are Bombshell Koopas which act pretty similar to normal Koopas except they explode a bit after they get stepped on.
Super Mario World
In Super Mario World it was finally a very unique species. As usual, Mario had to step on it to turn into a shell and be able to throw the shell, but now, the Koopa popped out of the shell, and was still able to hurt you or go back in its shell. Or Mario could just do a spin jump and the Koopa Troopa would vanish. Having Yoshi was a new element to the game, and the Koopa Troopa as well. As Yoshi, you could swallow them all up, or you could chew and spit. If Yoshi spits the green Koopa Troopa out, he spits out a shell.
If Yoshi spits out the red Koopa Troopa he would spit out three big balls of fire. If Yoshi chews and just keeps a blue Koopa Troopa in his mouth for a while he gets wings. If Yoshi keeps a yellow Koopa Troopa in his mouth, whenever Yoshi lands from a jump he causes an earthquake killing everything around him. One last addition to the Koopa Troopa is that once out of its shell, they could acquire the power of the Cape Feather, and fly through stages as Mario does when he also has Cape Feather.
Mario is Missing
In Mario is Missing, Luigi would jump on it to gather artifacts and coins.
Mario's Time Machine
It appeared once again in Mario's Time Machine as an enemy.
Super Mario World 2: Yoshi's Island
In Super Mario World 2: Yoshi's Island, it was Yoshi's enemy. Koopa Troopa could either be swallowed and turned into an egg, or be jumped on to get taken out of its shell, or it could be shot at with an egg to get rid of it.
Super Mario 64
In Super Mario 64, the Koopa enemies in this game would run away from Mario instead of attack him, and if Mario jumps on the Koopa's shell, he would ride on it.
Paper Mario series
In Paper Mario they were as flat as paper and only came out in red and purple (Dark Koopa), and had shades on. Mario would have to jump on it to lower its defenses and the jump on it some more to get rid of it for good.
In Paper Mario: The Thousand-Year Door, it once again was as flat as paper, and came out in red, purple (Dark Koopa), yellow (KP Koopa), and blue (Shady Koopa), and once again with those stylish shades.
Mario Power Tennis
Koopa Troopa reappears in Mario Power Tennis as a playable character, where he is classified as speedy. His Offensive Powershot is the Water Bomb, where Koopa performs a special drop shot that forces the characters to get close to the net. His other special move, the Defensive Power Shot named Water Shell Dash, consists of saving the loose ball by hiding into his shell and homing into the ball to make the return. Paratroopa is also present in this game. Koopa Troopa's default partner is Yoshi. Koopa Troopa's Mario Power Tennis trophy animation begins with him walking on stage with Luigi, Mario, and Peach congratulating him for his victory; Diddy Kong is also there, eating bananas. He then throws a banana peel in Koopa Troopa's path, unaware of where he is walking; and with Koopa Troopa not paying attention to what's in front of him. Mario, Luigi, and Peach try to warn him, but he slips onto his shell and slides across the stage, ricochets off a pole and hits Luigi in the head, making him drop the trophy from the impact. Koopa Troopa then catches it.
Mario & Luigi series
They are hardly prevalent in this series due to the games mostly taking place outside the Mushroom Kingdom
Super Mario Sunshine
They appear as Electro Koopas in Super Mario Sunshine in Pinna Park.
New Super Mario Bros.
Koopa Troopas reappear in this series much like their early iterations. However, they now stand on their hind legs. Most are still rather dim witted cowardly, falling off cliffs and retreated to their shell after being stepped on. They do dance to the music occasionally.
Super Mario Galaxy games
Koopas walk on four legs and sometimes come in red shells or green shells. They are mostly harmless and most of their appearances were as ammo.
Super Mario 3D Land
They reappear as enemies, taking on a similar behavior as in the New Super Mario Bros. series. Getting them trapped in a shell and bouncing it against the wall without touching the ground can be used to gain extra lives.
Super Mario 3D World
In Super Mario 3D World, Koopas reappear as enemies and act similarly to their appearance in Super Mario World. If they lost their shells, they would chase after them until it was too far out of reach. Players could take their shell and ride in them.
Super Mario Odyssey
Koopa-Troopas appear in Super Mario Odyssey, but not as enemies. Instead, they host special events. Most notable are the Roving Racers, who host the Koopa-Freerunning minigame. Another Koopa gives Mario a Power Moon when he goes in a near-perfect circle. Koopas also appear as enemies in the 2-D sections, acting exactly like in Super Mario Bros.
|Notable Koopas||Bowser • Bowser Jr. • Dry Bowser • Hookbill the Koopa • Iggy Koopa • Jr. Troopa • Kamek • Kammy Koopa • Koopa Bros. • Koopa the Quick • Kooper • Koopie Koo • Koopley • Koops • Kroop • Kylie Koopa • Larry Koopa • Lemmy Koopa • Ludwig von Koopa • Morton Koopa Jr. • Roy Koopa • Wendy O. Koopa|
|Koopa Troopa Species||Ankoopa • Boomerang Bros. • Dry Bones • Fire Bro. • Hammer Bro. • Koopa Troopa • Koopa Paratroopa • Koopatrol • K.P. Koopa • Lakitu • Magikoopa • Shady Koopa • Super Dry Bones|
|Major villains||Donkey Kong | Bowser | Foreman Spike | Wart | Koopalings (Ludwig von Koopa | Lemmy Koopa | Roy Koopa | Iggy Koopa | Wendy O. Koopa | Morton Koopa Jr. | Larry Koopa) | Tatanga | Virus | Wario | Kamek | Baby Bowser | Smithy | Big Bob-omb | Whomp King | Waluigi | King Boo | Shadow Mario | Petey Piranha | Bowser Jr. | Cackletta | Fawful | Antasma | Sir Grodus | Lord Crump | Shadow Queen | Princess Shroob | Count Bleck | Dimentio | Pom Pom | Boom Boom | Bowser Soul | Topper | Hariet | Rango | Spewart | Madame Broode|
|Minor villains||Blooper | Bob-omb | Boo | Bullet Bill | Buzzy Beetle | Chain Chomp | Cheep Cheep | Dry Bones | Goomba | Hammer Bros. | Koopa Paratroopa | Koopa Troopa | Lakitu | Magikoopa | Monty Mole | Ninji | Piranha Plant | Pokey | Shroob | Shy Guy | Snifit | Spiny | Thwomp | Whomp | Wiggler|