Dr. Yoshiyoki, born Dr. Yoshiwaru, is a Yoshi scientist and one of your partners in Paper Mario: The Diamonds of Virtue. His name comes from "Yoshi" and a yoki, a Japanese word meaning "expectation". His former name, "Yoshiwaru", is a portmanteau of "Yoshi" and warui, which means "bad".
Dr. Yoshiyoki used to be an evil scientist, but a lab accident turned him good. His brother Mitsuno was glad this accident occurred, because he was basically enemies with his own brother up until then.
The color of his eyes depends on when you meet him. His eyes will be red, blue, gold, or green. Every 15 minutes after the start of the game, his eye color changes, beginning with red.
Default attack: 'Chemical Attack
Description: Attack any one enemy with a liquid chemical and possibly poison it.
Action command: Press the button that appears on the screen.
Default attack: Blind
Description: Throw chemicals in an attempt to blind enemies briefly.
Action command: Press the 2 button with good timing.
Weaknesses: No known weaknesses.
Level A attack: Quintuple Reaction
Description: Yoshiyoki presses a button that causes up to five chemicals to react.
Action command: Press the buttons in the order they appear.
Level S attack: Scary Laugh
Description: Yoshiyoki recalls his days as an evil scientist. He holds a flashlight up to his face and laughs, scaring enemies away.
Action command: Repeatedly tap Z.
Weaknesses: Relies somewhat on luck. Sometimes this attack will miss, but very rarely.