When Soul Warden enters the battlefield, Pandemonium triggers, dealing 1 damage to you.
Darien triggers, creating a 1/1 Soldier creature tokens.
When the Soldier enters the battlefield, Pandemonium and Soul Warden trigger.
Resolve the Soul Warden trigger, causing you to gain 1 life.
Resolve the Pandemonium trigger, dealing 1 damage to you.
Repeat from step 3.
This clever loop turns the self-inflicted damage of Pandemonium into an unstoppable engine for creation and life. With Soul Warden on the field to cushion the blow and gain you life from every new arrival, Pandemonium's entry trigger deals damage to you, which Darien, King of Kjeldor translates directly into a fresh 1/1 Soldier token. That token's arrival triggers both Soul Warden and Pandemonium all over again, sustaining a perpetual cycle that yields infinite creature tokens, infinite creature entry triggers, and infinite life.