Prismatic gear

The seventh tier, above Legendary and Unique. The rarest gear in the game, and the whole server hears about every piece.

Where it drops

The Descent, from floor 5: from a floor's chest and, more often, from its boss. The chance starts very low and grows with depth.
The PvP world bosses: Old Hush, the Unrung Bell, The Hollow King, Vharoth, the Deep Colossus.
Never from the Rift of Ash or an ordinary monster, and Magic Find doesn't change the chance. A slow bad-luck counter does: the longer you go without one, the better your odds (at most double).

A Legendary-strength roll, with item level +1 and base stats 1.62x (Legendary is 1.55x).
One prismatic line, the last line on the item.
A random unique trait: the effect of an existing unique (weapon traits on weapons, armour and jewellery traits elsewhere). It never stacks with the same unique.
A place in a set: a real piece of a set for its base, else a wildcard piece of a set its wearers collect.
Every socket its base can have.

Elemental Shift: each hit adds X% as the next element (physical, magic, holy)
Chromatic Ward: a hit of 12%+ of your health gives a X% health shield for 6 s (every 20 s)
Spectrum: +X% damage, then X% less damage taken, then +X% healing, turning every 10 s
Refraction: X% chance a hit splits onto a second foe nearby for half
Prism Burst: a critical hit bursts for X% of it on foes within 4 m
Lumen: a kill heals you for X% of your health (every 4 s)

Prismatic gear is not bound: trade it, list it at a stall, bank it, or sell it to a merchant.
Party loot always opens Need / Greed for a Prismatic.
Salvaging one gives 2 or 3 Prismatic Shards. At the Blacksmith, Refract rerolls the prismatic line for shards and gold.
Every drop is announced once, server-wide: a System line with the linked item and a banner on that map.
Worn Prismatic gear doesn't glow on your character: the look comes from your costume, as for every tier.