Glad you enjoyed it!
The visual effects are all very simple. Simple to replicate in Unity, at least.
The main cool effect that I used for the skybox and the weird cubes is done by sampling the players current screen, and using that as a texture.
So the skybox is just a replication of what you are currently seeing, and so are all those mirror/box things. It gives a cool inception-ish effect.
Only thing that annoys me about it is how to skybox immediately turns pitch black if you look at it.
I also pixelated the screen and added some chromatic aberration as a post-processing effect.