Cast Kor Skyfisher by paying 0 and 2 life due to Defiler of Faith and Oketra's Monument.
Defiler of Faith and Oketra's Monument trigger.
Resolve the Defiler of Faith trigger, creating a 1/1 Soldier creature token.
When the Soldier enters, Virulent Emissary triggers, causing you to gain life.
Resolve the Oketra's Monument trigger, creating a 1/1 Warrior creature token.
When the Warrior enters, Virulent Emissary triggers, causing you to gain life.
Resolve Kor Skyfisher. When it enters, it and Virulent Emissary trigger.
Resolve the Kor Skyfisher trigger, returning it from the battlefield to your hand.
Resolve the Virulent Emissary trigger, causing you to gain life.
Repeat.
This ingenious loop turns a single white creature into a self-sustaining engine by completely eliminating its mana cost. With the cost-reduction powers of both Defiler of Faith and Oketra's Monument working in tandem, you can cast Kor Skyfisher for free by trading life instead of mana. When the Kor Skyfisher enters the battlefield, its own drawback forces it to bounce back to your hand, but every token generated along the way is pure profit—thanks to Virulent Emissary, each arriving ally conveniently gains you life to offset the cost of the Defiler.