Maps containing a Delirium Mirror can have the mirror walked through to unleash the rolling Delirium fog ring across the current area.
You must stay within this fog as it expands to maintain the Delirium or it will disappear.

Magic monsters are able to gain Delirium specific Modifiers while inside the fog.

Rare or Unique monsters in the fog may manifest Delirium Demons. Manifested Delirium Demons inhabit the monster's body to occasionally use Skills of their own.

Fractured Mirrors may be found within Delirium Fog, summoning extra monsters while Fracturing Mirror Shards are found at set depths, with more varied rewards.

Defeating Map Bosses has a chance to summon a Grand Mirror on a nearby map.

Fracturing Mirror Shards are a type of Fracturing Mirror found within Delirium Fog at set depths.

Escalation Shards may add modifiers to rare Delirium monsters, summoning more difficult and rewarding monsters, or pausing the Fog.

Deceptive Shards summon Delirium bosses or lead to an extra Delirious area.

Capricious Shards do not manifest by default, once unlocked they may summon a mirrored Map Boss, or cause Map Bosses to manifest Grand Mirrors.