Dr. Shroob

From the Super Mario Wiki

A Dr. Shroob holding up a Mushroom that he can use to grow to gigantic proportions.

A Dr. Shroob.

Dr. Shroobs are yellow Shroobs that wear thick, swirly glasses in Mario & Luigi: Partners in Time. During the Shroob invasion of the Mushroom Kingdom, Dr. Shroobs were stationed in the Vim Factory, allowing them to monitor the factory's vim transformation process. In battle, Dr. Shroobs attack with a ray gun (just like a regular Shroob). The energy blasts that result from this attack can be jumped over. Dr. Shroobs also like to use two items in battle: bio-engineered red Mushrooms and bio-engineered gray Mushrooms (perhaps relatives of the Poison Mushroom). The red Mushrooms will make Dr. Shroob gigantic, while gray Mushrooms will make the doctor tiny. After eating a Mushroom (regardless of color), the Dr. Shroob will then attack by charging into its opponent, inflicting heavy damage if big or minimal damage if small. Regardless of size, a Dr. Shroob's charge attack can be countered with a Hammer strike. Additionally, a Dr. Shroob will hold its Mushroom in its claws for a turn before using the item. As such, if the Shroob doctor is attacked while holding a mushroom, the doctor will drop the item.