Activate Wildwood Mentor using Marath's ability by paying 1 and removing a +1/+1 counter from it, creating a 1/1 Elemental creature token.
When the Elemental enters the battlefield, Wildwood Mentor's first ability triggers, putting a +1/+1 counter on itself.
Activate Ashnod's Altar by sacrificing the Elemental, adding CC.
Repeat.
Once you have infinite mana, you may forego sacrificing the Elementals.
This clever loop turns Marath, Will of the Wild into a one-person token factory by leveraging Agatha’s Soul Cauldron to grant Marath’s activated abilities to the board, while Agatha's Soul Cauldron simultaneously fuels those activations with any color of mana. Wildwood Mentor makes sure that every time you generate a token, you're rewarded with a fresh +1/+1 counter to keep the chain going, feeding right back into Marath's counters. Finally, Ashnod's Altar is the engine that converts your newly minted tokens into the colorless mana needed to fund the cycle, leaving you with an unstoppable cascade of infinite mana, tokens, and triggers.