Physiology & Features
- Mercury is partially horse, but partially replaced with rocket parts.
- Although Mercury doesn't need to be stuck with spurs to know to move, he does need to be told "Hi-yah!"
- Although he is an intelligent horse, he still needs to have a person steer him.
- He has pistons, which are useful for things like getting out of giant spider's webs.
- He is equipped with Wi-Fi.
- When necessary, he can operate with a sidecar.
- He has shields which can be activated remotely by Sparks Nevada.
- He cannot read, because he is a horse.
In She Blinded Me with Technology, a still-depressed Sparks Nevada learns Mercury can talk, and sings the song Riding the Galactic Trail with him at Mercury's insistence. After the song, Mercury and Sparks go looking for the reason Mercury is able to talk. After escaping from Kevin's spider trap, Mercury and Sparks defeat Technos the Advanced's Technologobots, and Sparks gets Kevin to reconsider his blood oath. Sparks and Mercury end the episode with more singing.
In Space-iversary, Mercury takes Sparks to his Space-iversary party, wherein they encounter Sparks' parents. Mercury encourages Sparks to confront his parents and gain their respect, and to beam aboard their spaceship with them. Later, as Sparks attempts to save a spacecraft from MurderMen, Mercury assists Sparks to help him win the day.
In Companeros, Sparks has grown tired of Mercury's constant chatter and need for attention. When Croach the Tracker returns and save Sparks' life, Mercury is jealous and upset, especially when Sparks is about to declare Croach as his best friend. To draw attention back on himself, Mercury declares he is about to be no longer able to speak, despite Croach's insistence that the radiation allowing animals to talk on Mars is not dispersing. Sparks does not give Mercury the attention he desired, and he has not spoken again except to say "Whinny!"
- "I'm a horse. With rocket parts!"
Although Mercury "appears" in many Sparks Nevada episodes as Sparks mentions riding him, Mercury is voiced in several episodes as well.
After Mercury ceases speaking, he can be heard saying "Whinny" several times. Rather than being played live by the actors in these segments, this is a sound effect recorded by Andy Daly.
- War of the World (TAH #53) - Mercury says "Whinny!" when Sparks asks him to confirm that he is or was able to talk.
- Mutiny on the Bounty Hunter (TAH #91) - Mercury speaks again in this episode, though he again only says "Whinny!", it may be in response to Croach saying that the horses don't comprehend human English.
- The Complete “Christmas on Mars” show from December 8, 2012 (TAH #147) - Mercury again says "Whinny!" when Sparks tells Mercury he doesn't have to explain himself to Mercury, as he's just a horse.
- Mercury also appears in the Sparks Nevada, Marshal on Mars segment of the Original Graphic Novel.
- Flood at First Sight (SNMOM #0)
- The Sad, Sad Song of Widow Johnson, Part One (SNMOM #1)
- The Sad, Sad Song of Widow Johnson, Part Two (SNMOM #2)
- The Sad, Sad Song of Widow Johnson, Part Three (SNMOM #3)