It is a small gopher with gray fur.
It seemed interested in the corn husk doll's hat. It bit Scooby when he tried to get it back.
Scooby-Doo and the Witch's Ghost
The hat from a corn husk doll which Scooby-Doo tried on, blew off and landed next to a gopher hole. A gopher then popped up and took it back down with him. This angered Scooby and he stuck his hand down to get it back, but was bitten by the gopher.