Food Chain + Mana Echoes + Marath, Will of the Wild

Mana needed: {R}{G}{W} plus enough mana to pay for commander tax, if applicable

RGW identity

Commander legal

The 3 combo pieces

Cast Marath by paying {R}{G}{W} plus commander tax, if applicable, causing it to enter the battlefield with a +1/+1 counter on it for each mana spent to cast it.
When Marath enters the battlefield, Mana Echoes triggers, adding {C} for each Elemental and/or Beast you control.
Activate Marath by paying {1} and removing a +1/+1 counter from it, creating a 1/1 Elemental creature token.
When the Elemental enters the battlefield, Mana Echoes triggers, adding {C} for each Elemental you control.
Repeat from step 3 until Marath has one +1/+1 counter on it.
Activate Food Chain by exiling Marath, adding {R}{R}{R}{R} that can only be spent to cast creature spells.
Choose to return Marath to the command zone from exile.
Activate Food Chain twice by exiling two Elemental tokens, adding {G}{W} that can only be spent to cast creature spells.
Repeat.
Once you have infinite mana, you may cast Marath for an arbitrarily large number of mana, and use its ability to put infinite +1/+1 counters on creatures you control and/or deal infinite damage to any target(s).