They are X-Naut doctors that develop many of the X-Naut's arsenal of weaponry and advanced technology. Led by Sir Grodus, they are a part of the X-Naut alliance and are found in the X-Naut Fortress.
In battle, X-Naut PhDs can use various chemicals. They can attack either Mario and his partners or even use their chemicals on themselves or allies. Their attack is broken into five different attacks of different colors.
X-Naut PhD's Stats (Paper Mario: The Thousand-Year Door)
Blue which makes themselves dodgy.
Orange which recovers ten HP to themselves or one of their allies; five HP to themselves and one of their allies
Purple which does three damage to Mario and can shrink him