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 Loading Zone and Pir, 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 explosive loop kicks off by activating Terra, Magical Adept's Trance ability to flip it into Esper Terra. Thanks to the doubling effects of Loading Zone and Pir, Imaginative Rascal working together, Esper Terra enters with an overwhelming number of lore counters, instantly triggering its fourth chapter. This grants you a massive injection of all five colors of mana while exiling Esper Terra and returning it to its front face. When Terra, Magical Adept enters the battlefield anew, its ability mills five cards and sets you up to easily repeat the entire cycle for infinite mana, self-mill, and continuous triggers.