Kammy Koopa
First introduced in Paper Mario, Kammy is an old Magikoopa who works for Bowser. Although she is a "bad" character, she added to the charm of her debut game. For example, she once said, "I'm a beautiful Koopa with a beautiful name!"
Kammy presumably oversees the Magikoopas, as one looked forward to getting a raise from Kammy for defeating Mario. Other duties that we have seen include plotting with Bowser and inventing a machine to buff up the Koopa king. Kammy's only attack in Paper Mario was to form yellow blocks and smash them down on enemies. In Paper Mario: The Thousand-Year Door, she attacks like a Magikoopa.
Kammy is described in by Goombario in Paper Mario as "the brains behind Bowser" and is high up in the Koopa hierarchy. Although Bowser makes cutting remarks at her, such as calling her a hag, Kammy seems to be getting a crush on him.
Kammy reappeared in Paper Mario: The Thousand-Year Door, which means it is unlikely that she will become a "forgotten character" like, for example, Tumble from Mario Party 3.