The Mystical Organ is available as one of the options through the Horror Circus Selection Kit which also allows to upgrade the Mystical Organ to level 2, thus improving its properties.
The Mystical Organ comes with the special set bonus. When it is adjacent to other buildings belonging to the Horror Circus Set the properties of the building are improved.
For more information see Set Bonuses.
The Mystical Organ can be upgraded by Mystical Organ Upgrade Kit item. To upgrade the Mystical Organ, use the Mystical Organ Upgrade item on the Mystical Organ that is already situated in your city. Its upgraded version will then be placed directly on the same spot in your city and the production timer will not be reset. Note that the upgraded building will be from your current era, even if the old one was from one of the earlier ages.
Mystical Organ will produce the following effects. Base effects will always be produced. Bonus effects are determined by how many other unique Horror Circus Set buildings it is connected to.