The Keystone Halo is a Demon Unique relic with no boss attached: it drops anywhere in Nightmare, most often from N4 up (rarer below that home difficulty, never above it), and nowhere else. Every copy is item level 100, and there 0.3% of what falls comes up Unique. It is built on Eternal Keystone Relic — step 6 of the Keystone Relic line, item level 80 and up.

It always rolls the same numbers: +10% Ultimate Generation, +10% Stone Damage, +12% Ultimate Generation, +12% Stone Damage, +54% Ultimate Generation, +492 Maximum Health and +50% Healing Power.

One Unique drop in 40 is a Mythical copy: the same item carrying 15–25% Mythical Energy that boosts every stat on it and can never be changed; the 15% floor is 10 times as common as the perfect 25%.

On top of that it carries The Keystone Halo — Ascendant Form heals 18% of max health instead of 10%, over twice the radius, for 2 more allies.

It fires Mason's Eye on its own: Every 5th critical strike cracks the target's guard, building Crumble for 60% of the hit.

Wearing it hands you Ascendant Form.

“Hold the arch up and the arch holds everyone.”