Mystery Boss Summoning Key

The Mystery Boss Summoning Key is a wildcard key that opens into one of the four boss summoning keys.

Open it and you'll get one key at random — an even shot at Lamia's Tear, Echidna's Coil, Thanatos' Idol, or Hephaestus' Sigil. Whichever you land on lets you go summon that boss and fight it for its loot.

Where to get it: an uncommon find in the Fund II–V lootboxes, guaranteed in the KOTH Lootbag (plus a shot at more from its pool), and turns up on the Black Market Auction House, from Erebus Pit guards, and at the Oracle.