Big, Gray, Shaggy Episode 1 (1971)

A puppy sees a big, gray, shaggy thing on the river, gets frightened and runs away, but on the way a chicken, a duck and a bear cub join him. They run to the little mouse, who is not afraid, but saw the fog in the big, gray, shaggy one. Do not be afraid of anything, and all fears will dissipate like fog.