Night of the Living Dummy vol 1 by R.L. Stine (Author)

Lindy names the ventriloquist's dummy she finds Slappy. Slappy is kind of ugly, but he's a lot of fun. Lindy's having a great time learning to make Slappy move and talk.

But Kris is jealous of all the attention her sister is getting. It's no fair. Why does Lindy always have all the luck?