Nim Deathmantle | Ashnod's Altar | Ashaya, Soul of the Wild

(and one other card)

Activate
Ashnod's Altar by sacrificing
Ashaya, adding ({C} magic symbol) ({C} magic symbol) .
When
Ashaya dies,
Nim Deathmantle triggers, causing you to pay ({4} magic symbol) to return
Ashaya from your graveyard to the battlefield, and attaching
Nim Deathmantle to it.
When
Ashaya enters the battlefield,
Sporemound triggers, creating a 1/1 Saproling creature token.
Activate
Ashnod's Altar by sacrificing the creature token, adding ({C} magic symbol) ({C} magic symbol) .
Repeat.
If you control a nontoken creature that has haste, you may instead sacrifice it, and then tap it each iteration to get infinite green mana and colorless mana.