Activate Terra, Magical Adept by paying 4 and tapping it, exiling it and returning it to the battlefield as Esper Terra.
When Esper Terra enters the battlefield with four lore counters on it due to Doubling Season and Innkeeper's Talent, its fourth chapter ability triggers, causing you to add , and then exile Esper Terra and return it to the battlefield as Terra, Magical Adept.
When Terra, Magical Adept enters the battlefield, it triggers, causing you to mill five cards and return up to one enchantment card from among them from your graveyard to your hand.
Repeat.
This intricate loop kicks off by activating Terra, Magical Adept's Trance ability to transform it into Esper Terra, taking advantage of Doubling Season and Innkeeper's Talent to immediately flood the Saga with double the lore counters. This massive counter-doubling instantly skips straight to Esper Terra's fourth chapter ability, generating a massive influx of all five colors of mana while exiling the Saga and returning it back to its front face as Terra, Magical Adept. When Terra, Magical Adept re-enters the battlefield, its triggered ability lets you mill five cards and potentially reclaim an enchantment, leaving you primed to pay the transformation cost and repeat the entire sequence for infinite mana, self-mill, and continuous entries and leaves-the-battlefield triggers.