Ghired, Mirror of the Wilds | There and Back Again | Umbral Mantle

Cards

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
Ghired by tapping it, creating a copy of the Smaug token.
Put either Smaug token into your graveyard due to the legend rule.
When the Smaug token dies, it triggers, creating fourteen Treasure tokens.
Activate three Treasure tokens by tapping and sacrificing them, adding ({3} magic symbol) .
Activate
Ghired by paying ({3} magic symbol) and untapping it, giving it +2/+2 until end of turn.
Repeat from step 3.

Once you have infinite mana, you may instead use
Ghired to copy any other token(s) that entered the battlefield under your control this turn. You may also attach
Umbral Mantle to another nontoken creature you control to make it infinitely large.