Slappy the Dummy is a fictional character and antagonist in the Goosebumps children's series by R. L. Stine. He is one of the series' most popular villains and the main antagonist of the Night of the Living Dummy saga and a major villain in later series. He is also the main antagonist of the Goosebumps movie and its sequel. According to R.L. Stine in Goosebumps, Slappy is a "ventriloquist's dummy with a serious Napoleonic complex" that comes alive by these words: "Karru Marri Odonna Loma Molanu Karrano" (which roughly translates to "You and I are one now"), and they can be found on a sheet of paper in Slappy's jacket pocket. After coming to life, Slappy will try to make the person who brought him back to life serve him as a slave, to the point that he will frame that person for things that he does.
His personality can be described as a dangerous prankster, who loves to have fun terrorizing anyone who comes across him and trying to make them his slave.
While none of them do Slappy bad, I'll have to give my vote to Cal Dodd for giving me nightmares as a kid. (Helps that I actually owned a dummy as a kid.) Buuut, even if it's my personal vote, I will admit the acting is kinda hokey and the voice veers a bit into Meowth territory. I can't be TOO hard on a show from the 90's though.
Jack Black does a good job, and does a good job at slipping inside the sinister dummy, but Mick sounds a bit more polished and less put on. Even if this isn't Mick's first time subbing in for Black, I think he does more than just put on a good impression, he reaaaaally gets into the evil and I love it.