Yoob is a shroob-created Yoshi that came from a pink and green egg.
Mario & Luigi: Partners in Time
Once it hatched it started to terrorize the island where the Yoshis lived and began to devour them.
Yoob later appeared in the location in which the Mario brothers defeat Kamek and confront Bowser. It was trying to climb up but it was to high to reach. A Shroob uses a ray to extend Yoob's size then it devoured the Mario brothers. Inside of Yoob is a egg factory created by the Shroobs. Inside Yoob, at the dead end is Sunnycide. After the Mario brothers defeat it, the entrance opens. When the Yoshis, Baby Bowser and the Mario brothers exit, it presumably dies.
- Yoob bears a strong resemblance to Barney.