Aliens (Sue Ellen Moves In)

Brainy Aliens are a species of alien with large, bulgy brains.

Buster imagined that Sue Ellen was one of them in "Sue Ellen Moves In."

Although the 3-Eyed Aliens stole the snowball in "D.W.'s Snow Mystery," Buster imagined that the Brainy Aliens did it. At the end of "Return of the Snowball," it is revealed that they indeed did steal the snowball.

Buster imagined that they came to Earth to capture a human in "I Owe You One," and picked Arthur, but they allowed Buster to be taken instead because Buster owed Arthur favors and he really wanted to finish his book.