Following off Goosebumps candidate the Snatcher...
Who is he? What has he done?[]
Slappy the Dummy is pretty much the face of the Goosebumps franchise appearing as the main antagonists in the Night of the Living Dummy series and its spin-offs. According to Bride of the Living Dummy, Slappy was crafted by an evil sorcerer who then placed his soul inside of the dummy.
If the magic words "Karru Marri Odonna Loma Molonu Karrano" which roughly translates out as "You and I are one now," it brings the dummy to life and he attempts to make whoever brought him to life and their families his slaves. That is his primary shtick in the series of books revolving around him.
At first glance, this wouldn't be that bad...if not for a few things. For one, there are his multiple murder attempts on the protagonists and other characters in the books. Whether it be trying to bash them in the heads with a guitar, or trying to chop the head off a boy with a pair of garden shears, Slappy consistently shows himself off as a homicidal maniac whenever things don't go his way. In Bride, Slappy tries to murder an entire room of children if his demands of having a bride weren't met. Which segues to my next point.
Slappy...is kind of a not-too-subtle pedophile. In Bride of the Living Dummy, as I have mentioned, he threatened to kill an entire room of children if he did not receive his bride. When a doll named Mary Ellen is brought to life and offers herself to him, Slappy clarifies that he meant the young protagonist of the book. And when she refused? He hits her in the face, referring to it as a "love tap." Then you realize that the majority of the victims he tries to make his slaves are young girls.
Freudian Excuse? Mitigating factors?[]
None. As I have mentioned, Slappy contains the soul of an evil sorcerer, so no Made of Evil there. Slappy has moments where he is funny, but that is mostly because the Goosebumps series is notoriously cheesy. Slappy's murder attempts and the...um...pedophile bits are played seriously.
Slappy is also a recurring character in other books made after the original series completed its run. From there, Slappy is often known to assist the heroes, like one instance in Goosebumps Horror Land. Except, in that case, the villainous Menace was threatening to kill every character in the book including Slappy, so that was the reason why he helped them.
Heinous standard[]
Has one of the highest attempted murder attempts for a recurring villain including some attempts in gory fashion (cutting a boy's head off with garden shears for one). Also, his pedophilic tendencies also make him stand out.