Natsuhi Otonashi, formerly known as Natsuhi Bokerdole, is the main villain of the Yuki generation, and all of the Yoru generation, so far. She is a being who exists and doesn't exist at the same time, and thus can easily travel through time, timelines, and space. In episode 557, it's revealed that she has become a virus that has hijacked PriPara and a lot of Parajuku.
Evil things she does
Traps people helplessy in loops that last at least a million years.
Tortures her own younger brother, just for fun.
Uses her time alteration powers to create illusions that can meld truth and lies into one single concept.
She was going to be an antagonist from the beggining of her creation.
When creating her Yuki kept the concept "Villain that could go undetected for decades" in his mind.
She was originally going to be a much more minor antagonist than she is.