Prismatic Key

The Prismatic Key (in game, the Transgressive Prismatic Key) opens the prismatic chest for the Facet of Defiance Prismatic Fragment in The Pale Heart. The fragment is reached through the Transgression area of The Impasse, in a poisoned cave where the Darkness nodes refresh your Shielded from Darkness buff.

After three waves of shielded enemies are cleared by shooting their hidden eyes, a Tormentor boss appears and drops the key. The key unlocks the prismatic chest, which contains the fragment.