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, Haliya triggers, causing you to gain life.
Resolve the Oketra's Monument trigger, creating a 1/1 Warrior creature token.
When the Warrior enters, Haliya triggers, causing you to gain life.
Resolve Kor Skyfisher. When it enters, it and Haliya trigger.
Resolve the Kor Skyfisher trigger, returning it from the battlefield to your hand.
Resolve the Haliya trigger, causing you to gain life.
Repeat.
This delightful engine turns the modest Kor Skyfisher into a self-sustaining storm and token machine by leaning heavily on cost-reduction and enters-the-battlefield synergies. With both Defiler of Faith and Oketra's Monument reducing the creature's casting cost to zero and letting you pay life instead, you can continually replay the Skyfisher for free. Each iteration triggers Defiler of Faith and Oketra's Monument to flood the board with Soldier and Warrior tokens, which in turn feed Haliya, Guided by Light to generate an endless stream of lifegain triggers. Finally, the Kor Skyfisher's own entry trigger forces you to bounce it right back to your hand, resetting the loop so you can repeat the process indefinitely.