Marath, Will of the Wild + Mana Echoes + Pir, Imaginative Rascal
Marath, Will of the Wild
Mana Echoes
Pir, Imaginative Rascal
Infinite colorless manaInfinite creature tokensInfinite damageInfinite creature ETBInfinite creature tokens that are infinitely largeInfinite +1/+1 counters on creatures you control
How it works
Activate Marath by paying 1 and removing a +1/+1 counter from it, creating a 1/1 Elemental creture token.
The Elemental enters the battlefield, triggering Mana Echoes, adding C for each Elemental you control.
Activate Marath by paying 1 and removing a +1/+1 counter from it, putting two +1/+1 counters on it.
Repeat.
Once you have infinite C, you may repeat step 3 to give Marath infinite +1/+1 counters, then use them to deal infinite damage to any target(s).