From the Super Mario Wiki
Janbi is a Nimbi from Super Paper Mario. His name is derived from January, just like many other Nimbis that have month and season derived names. He has no major roles, except for the fact that he is one of the Nimbis Bowser frees from the ice by using his Fire Breath.
That's Janbi. A young Nimbi. He's scatterbrained, so he's always running about. But he's also a sap, so at home, he and his girlfriend are annoyingly clingy.