#1 in a pair of not too bright scientists, who in the name of Dagget is "always trying to hurt us in the name of science". He has no canon name, which is a running gag to the point that when he gets a focus episode "Scientist #1" is in the episodes title.
Dr Stylish:
Possibly the gayest mad scientist to not appear in Rocky Horror, I honestly have no idea what this guy's first name is, or if Stylish is even his real last name, he's only ever referred to as "Dr. Stylish"
Buzz Kutt:
He appears to be a well respected scientist in the monster world, but his line about "conquering the humans" something no other monster seems interested in, seems to imply he's a mad scientist, even by their standards.
Noa Hiiragi:
Only in high school, but has an IQ over 200, and has a plan that involves altering the minds of everyone on the planet.
Dr Finklestein:
Literally the living embodiment of the concept of "Mad Scientist" in Halloween Town. I'm actually not sure if he has a Doctorate or not, but he's called "Dr. Finklestein" so Maybe?
Dr Werner Frank:
Inventor of FRANXX mechas the series is named after…. and also cloned and experimented on poor Zero Two when she was a child.
Vink:
He calls himself "Dr. Vink", but I am skeptical he is a licensed Doctor. Also insists he is not a "nutbag"
Fran Madaraki
Hey, the girl is a philanthropist and just wants to save lives by any means necessary! Its not her fault her creator / "father" never instilled in her concepts like "Quality of Life" or "Fate Worse than Death".