At the beginning of your precombat main phase, There and Back Again triggers, putting a lore counter on it.
There and Back Again's third chapter ability triggers, creating a legendary 6/6 Smaug creature token and causing you to sacrifice There and Back Again.
Activate Vitu-Ghazi Guildmage's second ability by paying ({2} magic symbol) ({G} magic symbol) ({W} magic symbol) , creating a copy of the Smaug token.
Put one of the Smaug tokens into your graveyard due to the legend rule.
When the Smaug dies, it triggers, creating fourteen Treasure tokens.
Activate four Treasures by tapping and sacrificing them, adding ({2} magic symbol) ({G} magic symbol) ({W} magic symbol) .
Repeat from step 3.
Once you have infinite mana, you may create infinite 3/3 Centaurs and/or copies of any tokens you control instead.