7/22/25- Even though the quest Nighthold: Into the Nighthold states the Nightshards drop form Normals bosses and up, it only drops from Mythic bosse and 1 run only grants 9 shards of 20.
Each boss can only give you a chance at Nightshards once per week, regardless of difficulty. The one exception to this is that if you defeat Gul’dan on Normal or Heroic, you can still engage him on Mythic and The Demon Within has an additional chance to drop a shard. So, the ideal farm is to clear one of those first, then do Mythic (skipping to Gul’dan to save time, if you can).
You can only loot shards from the first difficult you engage in, not from all of them each week. If you started with Mythic, and then went to Normal or heroic, you won’t get any from Normal and Heroic. Each boss has a chance to drop the a single shard, or a triple shard, but it is not guaranteed. My first week I cleared it I got 7. The second week I got 14. Its all based on that magical RNG, and sometimes you get screwed and sometimes you don’t. The quest will take you at least 2 weeks to finish, but realistically 3 or 4 depending on your luck.