It is believed that this kangaroo is named Agent K since all other agents are named by the letter at the start of their species (platypus = Agent P). The kangaroo was also seen in "It's About Time!" where she was watching Dr. Feelbetter, and in Isabella and the Temple of Sap. When Pinky took the elevator to his lair, at first it was clogged with agents, including the kangaroo. In Phineas and Ferb Christmas Vacation!, the usually straight face kangaroo was enjoying a Christmas party. This revealed that the kangaroo is a female, because there was a joey (Young kangaroo) in her pouch.
Its unknown if kangaroo has a nemesis, but in "It's About Time!" when most agents were siting beside their nemesis, kangaroo's nemesis was mostly out of view. (The man can be seen for a single frame at the beginning of the fight, revealing that he is an African-American with curly black hair.)