Yuina Himoo's introduction. One of her introductions involve the player character falling asleep in the classroom... only to wake up in a lab with her, being unable to move. Then she introduces herself as the Mad Scientist that wants to take over the world and using the player as human experiments.( Thankfully, she never does that anywhere in the game).
Tokimeki Memorial 4
Miyako Okura, the game's secret character. After repeatedly asking (an ominous thirteen times), the Protagonist convinces Miyako to go on a date with him. This event boosts her hopes, as she's always been in love with him, and now thinks the feeling is mutual. However soon after this date, the Protagonist makes an idiot remark how Miyako would make a lovely wife for another man. This shatters her psyche, as she begins to believe the Protagonist is screwing with her emotions. Once this happens, she will summon Robbie the Rabbit during your date with other girls. These attacks continue, even when Miyako is restored to normal. And she's unaffected by bombs...
Her Yandere theme sounds like something that should be in a Horror game instead of a dating sim.