Requires

Marath, Will of the Wild must be in the command zone. Mana Echoes must be on the battlefield. Phyrexian Altar must be on the battlefield. Marath, Will of the Wild must be your commander. Mana needed: plus enough mana to pay for commander tax, if applicable

Steps

1. Cast Marath from the command zone by paying and commander tax, if applicable, causing it to enter the battlefield with a number of +1/+1 counters on it equal to the amount of mana spent to cast it.
2. When Marath enters the battlefield, Mana Echoes triggers, adding for each Elemental and Beast on the battlefield.
3. Activate Marath by paying and removing a +1/+1 counter from it, creating a 1/1 Elemental creature token.
4. When the Elemental enters the battlefield, Mana Echoes triggers, adding for each Elemental on the battlefield.
5. Repeat from step 3 until Marath has one +1/+1 counter on it.
6. Activate Marath by paying and removing a +1/+1 counter from it.
7. Marath dies as a state-based action due to having zero toughness.
8. Choose to return Marath to the command zone from your graveyard.
9. Resolve the Marath ability, creating a 1/1 Elemental creature token.
10. When the Elemental enters the battlefield, Mana Echoes triggers, adding for each Elemental on the battlefield.
11. Activate Phyrexian Altar by sacrificing three Elementals, adding .
12. Repeat.
13. Once you have infinite colorless mana and Elemental tokens, you may cast Marath, causing it to enter with an arbitrarily large number of +1/+1 counters, and choose Marath's other modes instead.

Results