Phantomical

Description
Enemies are invisible while moving and not attacking; Any light source close to the player starts flickering.

Effects
Any time an anemy moves (AI based movement, not physical movement in itself) or attacks, he will slowly fade out over 1 second up until the previously mentioned conditions are no longer met (This excludes bosses and elite enemies, which do not fade at all).

It also makes any light which is close to the player flicker (rapidly "turning" on and off)

This makes the game more difficult by making it very hard to avoid contact damage, as well as avoiding putting oneself in a disadvantageous position.

Unlock Condition
Kill a total of 250 enemies which can become invisible.

These enemies include (but not limited to):
 * Enemies which literally become invisible.
 * Worm-type enemies which can indirectly hide inside terrain.
 * Enemies which have immunity phases, where the enemy is not directly visible. (such as The Reaver)

Trivia

 * Internally, this relic is called Relic_V_Phasmophobia.