The mirror was actually no problem as the playfield was aligned inversely to the mirror, while the printing on the Bumpers and playfield and other parts was similarly inverted relative to the mirror, so everything appeared normal and upright in the reflection.
But the advantage of the mirror was that it gave the ball the illusion of floating in deep water, or deep space, though the ball still moved at a more or less normal speed on a mini-playfield. The ball was also slightly smaller than regular pinballs, in order to stay proportional to the illusion of the playfield.
That reminds me of the game Krull, but there it was a normal lower deck mini-playfield with a normal sized ball just like Gottlieb's Black Hole, except that this Krull lower playfield was viewed through a reduction lens for the window which made everything look much smaller in the lower deck playfield.
I was lucky to have seen Krull also as it was placed at a major Southern California test location for the arcade distributor Betson Pacific, now Betson International. The location was Mar Vista Bowling in the late 70's through mid 80's and they at that time would have 5 or 10 brand new pinball designs on location Every Thirty Days, and they were open 24/7 back then.
The games that caught on stayed on as long as they made money while the losers were replaced with the next batch.
So when the machine disappeared from sight the next month, it was a pretty good indication that it was never going to be seen again/cancelled for production.
The Krull pinball machine was placed as a working prototype, but did not make the money from the players necessary to approve the design for commercial release and it was dumped the following month. I only played it once.