Biffidus

The Biffidus is a member of a tribe-like group of Biffidus, who act as anti-bodies within Bowser's body, and appear to assist the parasite worm Durmite. They are rounded in shape and carry spears, which they use to attack. During the events of Mario & Luigi: Bowser's Inside Story, Bowser ate a huge carrot which, unknown to him at the time, contained Durmite. The Biffidus assisted Durmite in battle, by trying to jab Mario or Luigi with their spears. However, after taking much damage, Durmite would eat the Biffidus, then regurgitate them at Mario or Luigi, which they must jump over the flying Biffidus. It is unknown why the Biffidus assisted Durmite, even though she ate them repeatedly, and considering that she was a "foreign body" inside of Bowser. However, the Biffidus were no match for Mario and Luigi, and were ultimately defeated, along with Durmite.

Biffidus X
While fighting Durmite X in the Challenge Node, several Biffidus Xs will come out to assist her. These act exactly as the regular ones do, except their stats are changed and they are gray in color instead of white.