Uber Uniques are a touchy subject in Diablo 4, as players aren’t too happy with their drop rates. One of the arguments was how difficult it would be to actually get one during the 3-month long seasons. Well, today we have a player that beat the odds and secured one of the best Uber Uniques for themselves!
Sasuke963_ managed to snag the Harlequin’s Crest aka Shako (named after the base helm type in Diablo 2)! And less than a month into the very first season of Diablo 4. This makes the helm the first reported seasonal Uber Unique in the game!
Sasuke963_ got the item in the Dead Man’s Dredge T40 Nightmare Dungeon, from the end of run reward on their level 78 Rogue. Also to consider, the Uber Uniques only start dropping at monster level 85. Due to that, a Seasonal drop is much less likely than on Eternal, where players are much higher levels generally.
While we have seen each of the 6 Uber Uniques drop on Eternal reams before, there is still one that has not shown itself. The new, 7th Uber Unique added with patch 1.1, As 
Ahavarion, Spear of Lycander is yet to be seen on Eternal or Seasonal characters (as far as we can tell). There have been bugged versions of it dropping, however, with no stats, but that bug was quickly fixed.
There are probably more Uber Uniques out there than have been reported, but this is the first one we’ve seen. So, congrats to Sasuke963_!