|This looks and feels like a really badly made flash game... but it's actually decent.|
The 2 screens are used to create dual mirrored platformer stages that you have to complete both at once using the same inputs. In some levels, the bottom screen character can de-sync from the upper screen character, so it really is like having to play 2 different stages at once. While other levels, they are tied together so both characters will stop moving if one runs into a wall. The former type of levels are way harder than the latter.
It's very short... the final level consists if you going through a vertical platforming stage, where you have to get the upper character to the top and the bottom character to the bottom so they can both put the mirror back in the pedestal at the same time... but then the top character temporarily breaks out of your control and makes you start the stage over from the beginning, only this time there's a time limit and the top character has inverted controls. This was the hardest part of the game... beating it was really satisfying.
But... that's still not the end. I guess there are some extra stages that you can unlock by collecting all the journals in the main stages. I got like, more than half the journals I think. Some of them are really hard to find. I don't really care about the story that is in the journals at all.