Shirley the Medium is a chihuahua who has a frequently occurring role on the show as an antiheroine. She is voiced by actress Mary Testa.
- Heterochromia in her left eye
- Large earring on her right ear
- Wears a green dress with a purple cape and blue hood
Shirley is a mystical fortuneteller whose primary pastime is casting curses on those who defy morality. She despises the greedy and the inhospitable, and subjects them to spells that only repair when their sins are reversed. Ironically, she is very fond of money; charging heavy fees on clients and selling herself on TV are some of the ways she obtains it. This is probably because she is poor (as shown in The Curse of Shirley). It may also be out of a desire to punish Eustace, whom she charges the most and whose actions annoy her the most.
- She refers to Eustace as "The Stupid One"
- She can play the saxophone, which she uses frequently as part of casting curses people who are greedy or defy morality or who's actions just plain annoy her, like Eustace.
- In Muted Muriel, it is revealed that she calls Eustace "The Stupid One" because Ma Bagge calls him "Stupid boy" and he calls Courage a stupid dog like Katz, Le Quack, The Puddle Queen, Big Toe, Mr. Weremole and Cajun Fox.
- She appears to have both an ironic sense of humor and a sense of romance. In Swindlin' Wind her curses are based on the crimes the couples have committed against her, and she removed them (without being asked) after seeing one member of the couple shows concern for the other, smiling as she does so.
Shirley's earliest known curse was brought upon famous pianist Velvet Vic, confining him within his own record in the episode Record Deal. The spell enabled him to escape only when the album was played, however she buried it deep inside a chest, removing that possibility.
Her services as a spiritualist are advertised on the Channeling Channel. It is in this way that she was found by Muriel and Eustace seeking to communicate with his deceased brother after warning him of the consequences of contacting.
When she offered her service to Eustace and Muriel after being called to contact Eustace's dead brother, she warned them both,"if you contact the dead for personal gain, there will be tragic consequences!"
- Shirley the Medium (debut)
- The Curse of Shirley
- Record Deal
- Swindlin' Wind
- Muted Muriel
- Aqua-Farmer (cameo)