[Autumn]

Then clearly the issue isn't Spirit Mirror but Mask of Metal and Mysterious. So lets give those the pipe instead.

The issue appears to be how Spirit Mirror interacts with Mask of Metal and Mysterious effects, and is not a direct outlier of mechanics that deny information such as the aforementioned effects. The former of which would be remedied by a visual indicator to Spirit Mirror itself, not directly nerfing its effect or usefulness but instead removing a fair bit of user error or otherwise cheese scenarios wherein you rely upon your opponent being undutiful or forcing them into what are definitively very unfair scenarios.