At first sight, the Mirlín is just a child's marble. But, it is the very firmament of the universe in which my worlds exist. The Mirlín exists out there somewhere, periodically passing between owners like any other marble. Each bearer of the Mirlín has contributed to its development, because of its unique power: it's powered by imagination.
The universe within the Mirlín came into being when one of its ancient owners imagined a universe within it. This came to pass: in the tiny glass ball, a "Big Bang" of imagination resulted. Now, in a little marble, an entire universe came into being, easily carried in a pocket. Stars and planets began to form, independent of events outside the Mirlín. Downalla emerged, and its history began.
The life-forms of Downalla and the Azabel System owe their diverse nature to the creativity of Mirlín owners. However, since the beginning, all peoples within this universe have developed independently. They are no longer subject to the control of external forces.
So, are the gods worshipped by people in this universe real? I don't know. They may be entirely artificial, imagined by different cultures to explain their existence*. The gods could also have been made at the time of the Big Bang, and thus only exist within the Mirlín. Or, most myseriously of all, the divinities people believe in could be extradimensional beings, who broke into the Mirlín using the Big Bang.
The contents of the Mirlín were first reveal to our "real" world in the later 17th Century. The Irish poet, Úna Ní Bhroin, experienced visions of what she called a Domhain Eile. She recorded her experiences in a manuscript, though received very little recognition in her own time. Almost nobody, it seems, believed her claims that the world she saw was real. Ní Bhroin's manuscript passed through the hands of several owners after her death. Downalla, the anglicised form of Domhain Eile, began to be used to refer to her visions. Jonathan Swift, a popular Irish author of this era, may have been influenced by elements of Downalla in his works.