Battle Trance is a Unique Amulet in Diablo IV Season 15. It drops from Astaroth.
Unique power
Frenzy gains the Barrage Variant for free and can stack 2 additional times. While at maximum stacks, you deal [50 - 66.66]%[x] increased damage and your other Skills gain [23.33 - 30]%[+] increased Attack Speed.
Affixes
Strength
+Ranks to Frenzy (1 - 3)
Lucky Hit: Up to a 20% Chance to Gain a Stack of Frenzy (one guide)
Where it drops
Astaroth (Lair Boss hoard - targeted drop)
Any Lair Boss general unique pool / world drop at Torment (chance rises per Torment tier)
Horadric Cube: Item Transmutation - Upgrade to Unique (Common base of same type + 1 Enhanced Primordial Dust + 10 Primordial Dust) rolls a random unique of that item category