This was one of the most frightening episodes in season four's dark theme.
The characters are being chased by a monster. However, the monster is shot live action, and has a rather disturbing appearance, with a deer head, gorrilla(?) body, red lights for eyes, and long hair (actually yarn) on its head.
The monster's presence is never explained.
Eventually, the monster is defeated.
They then go on a picnic and everyone acts as if nothing ever happened.