"The key lies in your reflection"
Buddy's reflection shows Chase, who, at this point, he believed he had to sacrifice in order to escape his situation and his past mistakes. In his dream, that is represented by him having to break the mirror to escape The Old Man.
Chase has a wish, but so does Buddy, and the latter cannot let the opportunity to save his family and erase his faults slip from his fingers.
What Buddy cannot see here is that the key to his salvation lies in his reflection. Because, despite currently appearing to be his main obstacle, it will be Chase who reunites his family and gives his dream of being human even more meaning.
It is through the reflections of Chase and Deacon that the path to where the information needed to solve the mystery is stored is revealed.
Buddy's reflection is what allows Chase to figure out the fact that he's a key.
Without this, it would have been almost impossible for him to understand it simply by looking at Buddy's features. The gemstones that Buddy and Violet have in lieu of irises are much more polished (instead of being cut into reflective facets like the other keys' eyes are), but without looking at Violet's human form in the mirror and understanding that the keys' gemstones can take many different appearances, it would not have been possible to relate Buddy's unique-looking eyes to the keys'.
The main enemy has always been present between our heroes, and the key to revealing this truth lies in The Old Man's reflection.
It's the most blatant demonstration of a simple answer to a million questions found through a simple medium in the whole series.
There have been many instances like this in the past, but never quite like this one. Wave's revelation as the main antagonist, who has been searched for by our characters from the very beginning, could not have been better shown through any other medium.
The key has always been found in the reflections shown all throughout the series, both literally (as I showed in these examples) and metaphorically.
What further symbolism might hold the manner in which this revelation has been given to us?
snowghoul
tangentwithtanner
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germansingergirl
