What the game says, what really changes when you play, and the code to unlock it. Steam says 4.3% of players have it.

Artifact of Delusion
Game text: «Risk your items after completing the teleporter event in a test of memory to gain more items.»
After completing the teleporter event, your items go into closed chests and you have to remember which one holds each. Guess right: you get them back and gain more. Guess wrong: you lose the item.
A memory minigame with your items at stake. Note which chest each item falls into before they close. It arrived with Seekers of the Storm.
It arrived with the Seekers of the Storm expansion. 4.3% of all Risk of Rain 2 players on Steam have it, from Steam's public stats on 31 October 2026.
Read top to bottom, as shown here: three rows of three shapes. Each slot on the generator changes shape when pressed, in this order: square ■, circle ●, triangle ▲, diamond ♦.
In co-op, the group can enable any artifact that any player has unlocked. Artifacts are chosen in the menu before the run starts.
Enter its code (■●■ / ●●● / ■▲■) in the Compound Generator on Sky Meadow or Helminth Hatchery, use the laptop and beat the Bulwark's Ambry trial: take the key and break the reliquary.
After completing the teleporter event, your items go into closed chests and you have to remember which one holds each. Guess right: you get them back and gain more. Guess wrong: you lose the item. A memory minigame with your items at stake. Note which chest each item falls into before they close. It arrived with Seekers of the Storm.
4.3% of all Risk of Rain 2 players on Steam have it, from Steam's public stats on 31 October 2026.
Sources: the game's English text (artifact name and description), the Risk of Rain 2 wiki (riskofrain2.wiki.gg: the Artifacts page and this artifact's page, read on 31 October 2026; code, Compound Generator and Bulwark's Ambry) and public Steam stats. The plain-words text is ours. Icons: Risk of Rain 2 (Hopoo Games / Gearbox).