Cast Whitemane Lion 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, Answered Prayers triggers, causing you to gain life.
Resolve the Oketra's Monument trigger, creating a 1/1 Warrior creature token.
When the Warrior enters, Answered Prayers triggers, causing you to gain life.
Resolve Whitemane Lion. When it enters, it and Answered Prayers trigger.
Resolve the Whitemane Lion trigger, returning it from the battlefield to your hand.
Resolve the Answered Prayers trigger, causing you to gain life.
Repeat.
This clever loop uses cost reducers to cast Whitemane Lion for free—reducing its generic mana cost with Oketra's Monument and its white mana pip with Defiler of Faith by paying 2 life. Every time you cast the Lion, both Defiler of Faith and Oketra's Monument trigger to flood the board with Soldier and Warrior creature tokens. As each of these tokens and the Lion itself enter the battlefield, Answered Prayers triggers to continually pad your life total while also transforming into a massive 3/3 flying Angel. Finally, Whitemane Lion's own entrance triggers its ability to bounce itself back to your hand, allowing you to recast the creature and repeat the entire sequence indefinitely.