The Koopa Troopa (Japanese: ノコノコ, Noko Noko) is a character that appears in the Mushroom Kingdom (universe) universe. It's also an enemy in Stage 1 of Adventure Mode, as well as a random occurrence in barrels and capsules in VS. mode.
Koopa Troopa walk back and forth around a stage. If you make contact with them of them then you will take damage. Simply just attack them to make them retreat into their shells. You can pick up their shells and use them like the Green Shell item. The only difference is that the shells from the Koopa enemy don't disappear. The reason is after a short amount of time Koopa will come back out of its shell and walk back and forth again. To permanently get rid of them you must throw them by picking them up with the "Z" button. You can throw them at your opponents to give them a good amount of damage and maybe even killing them at low percentages.