Ooh, I hc that he can see in the dark (the average one, not the Dark™), which is an ability he got as part of the all-seeing gift package after the first attempted Watcher's Crown. I once saw an art of him that depicted him with eyeshine like a cat (don't remember the artist), and the idea never left my head since.
Not even kidding I want this to be canon. That’s absolutely amazing and I’m 99% sure I’m never going to forget about this idea either omfg. Just imagining his eyes reflecting in the dark is enough to drive me crazy.