There and Back Again has exactly two lore counters on it.
({4} magic symbol) ({W} magic symbol) ({U} magic symbol) ({B} magic symbol) ({R} magic symbol) ({G} magic symbol) if you don't control a Smaug token available.
Steps
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.
If you control two Smaugs, put one into your graveyard due to the legend rule.
If you do, the Smaug that died triggers, creating fourteen Treasure tokens.
If you made Treasures this way, activate nine Treasures by tapping and sacrificing them, adding ({4} magic symbol) ({W} magic symbol) ({U} magic symbol) ({B} magic symbol) ({R} magic symbol) ({G} magic symbol) .
Activate Go-Shintai by paying ({W} magic symbol) ({U} magic symbol) ({B} magic symbol) ({R} magic symbol) ({G} magic symbol) and tapping it, returning There and Back Again from your graveyard to the battlefield with a lore counter on it.
There and Back Again's first chapter ability triggers, causing the Ring to tempt you.
Activate Contagion Engine by paying ({4} magic symbol) and tapping it, putting two lore counters on There and Back Again.
There and Back Again's second and third chapter abilities trigger.
Holding priority, activate Clock of Omens twice by tapping four artifacts, untapping Contagion Engine and Go-Shintai.
Resolve the second There and Back Again trigger, causing you to search your library for a Mountain and put it onto the battlefield.
Resolve the third There and Back Again trigger, creating a legendary 6/6 Smaug creature token and causing you to sacrifice There and Back Again.
Repeat from step 3.
Results
Infinite colored mana.
Infinite death triggers.
Infinite ETB.
Infinite LTB.
Infinite proliferate.
Infinite Treasure tokens.
Put all Mountains from your library onto the battlefield.
Infinite mana nonland permanents you control can produce.