This episode is very similar to Harvey's Civvy, episode 3x2 of Harvey Birdman: Attorney at Law.
In both shows, the protagonist is a super-hero who has moved into another field of work. The protagonist is being sued for damages caused in the past, whilst they were a super-hero. In both cases, the group of persons suing the protagonist are characters from the action-series. Also, both times, the lawyer suing the protagonist is a villain from the action-series.
This episode reveals Space Ghost's middle name to be Eustace. It's on the letter sent to him from Dr. Nightmare: Attorney at Law.
Space Ghost: Shyster!
Dr. Nightmare: Poltroon!
Space Ghost: Ambulance chaser.
Dr. Nightmare: No talent Hanna-Barbarian!
Jayce: Big meanie!
Zorak: Knish eater!
Moltar: uh. Bubbuly peg!
Space Ghost's accusation that Dr. Nightmare tried to steal his brain is probably a reference to an episode of the original Space Ghost series, when Dr. Nightmare tried to put SG's brain into an evil robot.
Space Ghost: Unjustly? You vibroshocked 3 galaxies out of existence. You stole fizzy lifting drinks! And then you tried to steal my brain!
In 1974's Willy Wonka and the Chocolate Factory, Charlie Bucket and Grandpa Joe diverge from the tour and drink the fizzy lifting soda. In a later scene, Wonka exclaims, "You stole fizzy lifting drink!"