The Maradan prison is where pets are confined when they have committed a crime. Your pet can go to prison if caught using illegal items. Any illegal jobs can also send your pet to prison. But not paying your electricity bills at the powerstation will definitely send one of your pets to prison.
If your pet is in prison below, you will have to two options. You can free your pet and pay the 2,500MP fine. Your pet will leave prison but will change colour into a prison coloured pet.
If you do not want your pet to change into prison form when it leaves the prison, you can bribe the prison guard, Corporal Knifejaw, with 15,000MP and it will escape unchanged.
None of your pets are currently in prison. Keep it that way!