There and Back Again and Song of the Worldsoul on the battlefield.
There and Back Again has exactly two lore counters on it.
({3} magic symbol) ({R} magic symbol) available.
Steps
At the beginning of your precombat main phase, There and Back Again triggers, creating a legendary 6/6 Smaug creature token, and causing you to sacrifice There and Back Again.
Cast Seething Anger with buyback by paying ({3} magic symbol) ({R} magic symbol) , targeting any creature you control.
Song of the Worldsoul triggers, creating a copy of the Smaug token.
Put a Smaug token into your graveyard due to the legend rule.
When the Smaug dies, it triggers, creating fourteen Treasure tokens.
Resolve Seething Anger, giving a creature you control +3/+0 until end of turn and returning Seething Anger to your hand.
Activate four Treasure tokens by tapping and sacrificing them, adding ({3} magic symbol) ({R} magic symbol) .
Repeat from step 2.
Once you have infinite colored mana, you may use Song of the Worldsoul's trigger to target any other token you control instead.