It's not optimal design from a player's perspective (where everything is useable and attainable easily), but black kat tends to sell and intrigue and honestly there are worse things. I know you won't like it Zero Chill but try to think outside the box and realize that this would both make money for the devs AND get us something cool and new.
Here are 2 sets and how to get them:
Serene Plate Armor (Ancient but fixed up and new and functional)
Stats on each piece:
+Normal resist (same as ancient plate)
+Piercing resist (same as ironmight plate's pierce)
+Elemental resist (same as volcanic plate's elemental)
+Status resist high (Fire, Shock, Curse, Stun, this is +3, not +4)
+10 HP per piece at level 10 (instead of the usual +5 at level 10)
+Damage high (all)
-Movement speed decreased (low)
-Attack speed decreased (low)
-Negative resist med (freeze, sleep)
How to get this incredible set:
+requires 6,000 tortodrone shells per piece
+requires 6 pieces of ancient (helm/armor for helm/armor, respectively) as material
+Upgrades from 4* plate
Obsidian Angel Set (Heavenly Iron except black + obsidiany)
Stats on each piece:
+Shadow Resist (same as ancient plate's normal)
+Elemental/Piercing Resist (Same as ironmight's pierce)
+Status resist (Poison, Curse, Fire: +6 per piece)
+MSI high
+Sword damage increased high
+Damage increased vs fiends high
-only 3 HP per piece at level 10 (instead of +5 at level 10)
-Damage reduced against non-fiends low
How to get this incredible set:
+requires 13 gremlonium
+requires 13 celestial ore
+Requires materials worth a total of 13K apocrean sigils
+Upgrades from 4* angelic set
On the surface this is an "oh no baby what are you doing" kind of post, but I had my brain surgically removed to be outside of the box, so thinking over there, this is actually a pretty interesting idea.
Obviously the stats can be tweaked a bit, but overall the idea for a "super set" that is abnormally hard to get with high power output is pretty cool.
I would say prices should be adjusted properly - while 6,000 ancient shells seems like a fair cost, that is roughly 1,500 tortodrone fights, which would be roughly 1 week straight of fighting tortodrones, assuming roughly 6 minutes per run. That is a bit too much to ask for - the amount of shells should reflect the winterfest scarf grind, which is around 18 hours of grinding.