What the game says, what really changes when you play, and the code to unlock it. Steam says 12.9% of players have it.

Artifact of Soul
Game text: «Wisps emerge from defeated monsters.»
Every monster that dies releases a blue wisp, which is a new enemy. They give no gold or experience and burn out on their own after 12 seconds.
More enemies and more pressure, with no reward: with Artifact of Sacrifice the wisps drop no items. Bad for melee survivors; Huntress's Laser Glaive bounces straight to the wisp that just spawned.
It is in the base game. 12.9% 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.
Every monster that dies releases a blue wisp, which is a new enemy. They give no gold or experience and burn out on their own after 12 seconds. More enemies and more pressure, with no reward: with Artifact of Sacrifice the wisps drop no items. Bad for melee survivors; Huntress's Laser Glaive bounces straight to the wisp that just spawned.
12.9% 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).