Moo-Ping 10 is first offhandedly mentioned by Zim in Issue 1 of the comic series, when he explains to GIR that Vortian Prisoner Number 777 has been moved there from his original prison on Vort. Apparently, it's dirtier there than on Vort.
The context of Zim first mentioning Moo-Ping 10 suggests that it's another Irken prison facility. However, when it finally properly appears in Issue 34, it's revealed to in fact be operated by the Gellaxis, a gelatin-based species which is obsessed with right angles. Due to this obsession, the prison (a station floating in empty space) is composed of numerous interlocking square components.
It's also revealed that Moo-Ping 10 is a for-hire prison, allowing people to lock up their enemies for a price. Zim himself pays to have numerous people incarcerated, including 777, Madness the Chihuahua, a large alien he's mistaken for Sizz-Lorr, and several others whom appear to be there for no other reason than Zim doesn't like them.
As Moo-Ping 10 serves as a for-profit prison, the Gellaxis operators are very strict about payments. When Zim fails to make his (due to putting the absent-minded GIR in charge of it), he is himself imprisoned until such time he can come through with the money; worse, since the aliens he had imprisoned wanted revenge, they stayed and repeatedly beat him up, much to the guards' frustration, as the wad he was beaten into upsets their obsession with angles.
Eventually, with the help of Zorphic, Zim is set free when it was revealed that his paything was in the Voot Runner all along.
In Invader Zim: Enter the Florpus, Zim imprisons Professor Membrane in Moo-Ping 10 when he kidnaps him and usurps control of his labs for his new plan. Dib and Gaz later arrive on Tak's Ship to rescue him, the Ship describing it as the "Prison of the Galaxy's most infamous criminals."
Dib and Gaz sneak aboard while the ship creates a distraction, only to be caught by the Gellaxis and tossed in a cell. Fortunately, it's the same cell that their father is being kept in, and the ship soon arrives to break them out and take them back to Earth.
- Vortian Prisoner Number 777
- Zorphic (Madness)
- Sizz-Lorr Look Alike
- The Skinbagsi
- G'raggo the Fondulant
- Octilius Primilus
- Officer O'Herlihey
- Nub Bubbins (Enter the Florpus)
- Professor Membrane (Enter the Florpus)
- Dib Membrane (briefly, Enter the Florpus)
- Gaz Membrane (briefly, Enter the Florpus)
- Zim (Temporarily)
Facts of Doom
- Ironically Moo-Ping 10 has a welcome sign of a happy face behind bars giving two thumbs up.
- Moo-Ping 10 operates very much like the standard image of a prison. This includes having all the prisoners wear matching orange jumpsuits, having a cafeteria area for shared mealtimes, and an indoor courtyard for exercise.
- Due to the Gellaxis' obsession with angles, the prison has guards specially trained to eliminate anything that wads up into masses without angles.
- Despite the fact that Zim mentioned that the prison is dirtier than Vort, that doesn't seem to actually be the case, due to the neat freak attitude that the Gellaxis species as a whole seems to share. This hints at the possibility that the prison was previously quite dirty and the Gellaxis are simply "new management".
- Some of the prisoners seen in Issue 34 are characters that have not been seen on the series or in previous issues of the comics. Adding in the dialogue of Zim gloating in their faces, this seems to suggest that he has had several "off screen" run-ins with other aliens across the galaxy.