Autumnal Crown is a Unique Helm in Diablo IV Season 15. It drops from Varshan (Echo of Varshan).
Unique power
Wind Shear now deals [225-300] Poisoning damage over 4 seconds. Lucky Hit: Wind Shear has up to a 20% chance to restore 100 Spirit.
Affixes
1,200 Armor
+[1-3] to Basic Wind Shear Skills (1-3)
Where it drops
World drop (any difficulty, drop rate scales with Torment tier)
Dedicated drop: Echo of Varshan (Lair Boss, Torment 1+; Boss Trophy: Malignant Heart)
Horadric Cube: Item Transmutation (Upgrade to Unique) - Common item of the same slot + 1 Enhanced Primordial Dust + 10 Primordial Dust (random Unique of that slot)
Horadric Cube: Item Transmutation (Amalgamation) - 5x Malignant Heart (Boss Trophy) rolls a Unique from this boss's pool; can roll Mythic quality with the 'Crafted' tag