The sender in the Return of Oz seems to be the Knob King. He is trying to literally ruin Oz and is almost successful when he turns them all to stone. Then he is slowly continuing to take if over inch by inch by having all the stones spy for him, and having evil wheelers act has his guard dogs. He clearly fits the sender function. Dorothy is the one who prevents him in ultimately killing of OZ entirely. She steps in saving the day, bringing everyone back to life, and diminishing the Knob King.