There's Miraak of course. The one in the mine with the Bloodskal Blade, right next to Raven Rock. Another one requires you to help a Dunmer mine some cave open, and after half a month of mining at earliest, you can grab the new mask. The Jailor, which needs a citizen of Skaal to activate the quest. No mask.
Then one in some random icy dungeon. Think it starts out with Rieklings until you get further in.
Beating FF Superbosses. 1-4, 6, After Years, and 13-2 completed. FF5: Ancient Library FF7: Wall Market