Night Of The Living Dummy III by R. L. Stine
They're baa-ack! Make way for the bestselling children's series of all time! With a fresh new look, GOOSEBUMPS is set to scare a whole new generation of kids. So reader beware--you're in for a scare! Trina's dad used to be a ventriloquist, and has an attic full of old dummies. Then a new dummy arrives. Suddenly there are voices in the attic, strange accidents, and dummies move around mysteriously. Of course there must be a logical explanation, because it's stupid to be scared of a dummy...isn't it?