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 Vorinclex, 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 clever infinite loop relies on the brilliant synergy between Esper Terra and its ability to immediately leap through its Saga chapters. When Esper Terra enters the battlefield, Doubling Season and Vorinclex, Monstrous Raider step in to double the lore counters placed upon it, causing its fourth chapter ability to trigger right away and yield an abundance of colored mana. That same chapter ability then dutifully exiles and returns the card as Terra, Magical Adept, whose entry trigger allows you to mill five cards and potentially salvage an enchantment from your graveyard. By paying into the Trance ability to transform it back into Esper Terra, you restart the cycle anew for endless mana, self-mill, and continuous triggers.