Wildheart Hunger is a Unique Boots in Diablo IV Season 15. It comes from World drop (any difficulty, drop rate scales with Torment tier); Dedicated drop: Astaroth, the Charred Duke (Escalating Nightmare Dungeon boss; Boss Trophy: Ash of the Charred Duke); 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).
Unique power
Rabies spreads 100% faster and deals 10%[x] bonus damage each time it spreads, up to [120-150%][x]. (Patch 3.2.1: Bosses always take the maximum damage bonus.)
Affixes
600 Armor
+[1-3] to Rabies (1-3)
Where it drops
World drop (any difficulty, drop rate scales with Torment tier)
Dedicated drop: Astaroth, the Charred Duke (Escalating Nightmare Dungeon boss; Boss Trophy: Ash of the Charred Duke)
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 Ash of the Charred Duke (Boss Trophy) rolls a Unique from this boss's pool; can roll Mythic quality with the 'Crafted' tag