Boss Essence

Boss Essence is a stackable summoning component, the raw material you collect to forge a boss summoning key.

Each of the four bosses has its own flavour-matched essence: Echidna (green), Lamia (purple), Hephaestus (gold) and Thanatos (dark purple), with art that glows brighter as your stack grows. Collect 96 of one boss's essence and the inventory sweep auto-forges them into a single Boss Key for that boss. A single stack holds 64, so you need a stack and a half. See Summoning a Boss.

Where to get it: dropped by Shades & Wraiths in private Polis runs. The Polis level you pick decides which essence drops: Lamia from level 1 (best up to about 70), Echidna from level 60 (best about 75 to 99), Thanatos from level 95 (best 100 to 101), and Hephaestus from level 100 (best 102 and up). Neighbouring essences overlap at the edges. See Hunt Tiers & Boss Essence.

Essence does not drop in the Erebus Pit, and there is no shop that sells keys any more. The Uber bosses don't use essence at all: their keys are separate relics from the Sacred Way.

Boss keys stack like any other item, and a stack you split in your inventory or your vault stays split.