Serra's Sanctum and magical mirrors
I like your idea. I know very little about the MtG universe, so I'm not sure what might be most helpful here. Some ideas that come to mind:
The 2x2 boat stud elements are available in trans-clear and might provide the sort of look that you are hoping for.

There is a mirror element (20193) available. This could potentially be used in a lens apparatus of some sort.

The 2x2, 3x3, 4x4, and 6x6 dish elements are all available in trans-clear, and they could be useful for designing a lens system.

There's also a variant of the 6x6 dish with a handle on the side instead of the studs in the center that might work better for your application.

As zovits pointed out, the 6x6 also comes in a half-sphere variant:

There are also many printed transparent dish elements that might provide the sort of look that you are looking for, such as something like this: