26. Darkest/saddest canon moment
You mean besides the cliff moment that we get to see in the first ten minutes and then, if that's not enough, have to see again with lots more detail and pain and heartwreck, at the end of the flashback?
Yeah, well. Besides that.
There are quite a lot (people we have learn to like or love die all over the place, in the war and after) but actually the scene that hurts me the most is
when Wei Wuxian and Wen Ning (accompanied by Lan Wangji - by this stage, that's a given) go back to the Burial Mounds in episode 44 and see for the first time since they both 'left' all those years ago the black and barren place it now is. Their small and desperate little group of refugees and innocents that they tried to save, that became a family for both of them, murdered and long gone; their poor and pathetic - but just for a little while safe - home, where they worked so hard to survive and simply stay out of trouble, is nothing more than crumbling ruins, black ash and dead lotus plants. The actors play it very quietly and I cry. Every time.
(click to enlarge)