This needs a stretch. (Feel free to remove when satisfied of completion.)
A haunting need for images
The Tar Monster was the disguise of Dean Drabwell. It seems that old man Grumper's land was worth a fortune, but he wouldn't sell it to Drabwell. So he devised a plan to scare Grumper into selling it to him. His wife was his accomplice in all this, as she dressed up as a zombie to aid in the executing of the plan. With this great master plan, he was going to get the old man to sign his land over to him.