X-Naut PhD's are enemies from Paper Mario: The Thousand Year Door. They are scientists in the army. They experiment with different chemicals to improve combat and they also create Yuxes. X-Naut PhDs wear lab coats similar to a real life scientists.
They will attack by drinking and throwing chemicals. The chemicals they drink improve health and attack power. The chemicals they throw burn, shrink, and damage Mario.
They are found in the labs and corridors of the X-Naut Moon Base such as in the Yux lab.