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 get one of the four normal keys at random: Lamia's Tear, Echidna's Coil, Thanatos' Idol or Hephaestus' Sigil. Whichever you land on lets you summon that boss and fight it for its loot.

It only ever rolls the four normal keys. Uber keys are separate relics and never come out of a Mystery Key.

Where to get it: the Fund II to V lootboxes, the KOTH Lootbag (5 at a time), the Oracle, quest rewards, clue caskets, rank kits, seasonal crates and some store loot boxes and bundles. Since the Boss Shop was removed in Map 4, boss keys only come from essence and from drops like this one.

It no longer drops from Erebus Pit guards, and it is no longer on the RNG Meter.