The dream-ego can be a funny thing. Your one saw what happened to the two others and acted as if, "oh, the middle mirror must be for me!" And the shadow, rather than being a match, was out of proportion. And then your dream-self turned the tables and ate the shadow when it otherwise would/could/should have eaten you.
The mirrors and shadows could represent something either illusionary or something way too true that can't be consciously seen. Not necessarily paranormal, although it can be that, just something perhaps that you can't consciously catch because it's shunted to a separate category. Rather than letting it master you or surprise you, you have mastered it.