Knock-knock- who's there?

Once in the mountains lived a bogy called Hadeor. He was quite small, but with a huge appetite. The others called him a MegaPie.
His friends decided to play a trick on him. They hid all the food in village and covered themselves with paint so that all the monsters paired up and hid themselves in caves.
They left a note to Hadeor: "Go knock on the doors, find us and then you will get a pie.". MegaPie's stomack was really empty and he agreed at once.
"Knock-knock, who's there," Hadeor yelled in front of caves. You could feel from his trembling voice, that he is not going last long without pies.
Help our hero to overcome his hunger and get food. Find all pairs of pranksters and MegaPie will thank you.