Mostly, the "not describable by physics" part, as I and maybe many others see it, is a logical impossibility, because physics is what describles real things. Laws of simulated physics can be manipulated, but it will still be within the 'real' physics of the real reality. Thus, not supernatural. At least, not in the sense that I understood the question when I answered it.

As for

Likewise, mental phenomena in a simulation may not be reducible to non-mental phenomena within the same simulation.

Can you expand this one?