The Eightfold Idol is a Unique Ring in Diablo IV Season 15. It comes from Beast in the Ice (Lair Boss loot table) - one guide S13 guide.
Unique power
Blazing Scream leaves Sigil of Subversion Shadow or Lava trails behind. You deal [60 - 80]%[x] increased Abyss or Hellfire Skill damage to enemies on Sigil of Subversion trails, based on the trail's type.
Affixes
Willpower
Skill Ranks to Sigil of Subversion
Where it drops
Beast in the Ice (Lair Boss loot table) - one guide S13 guide