Activate Ashnod's Altar by sacrificing Pelakka Wurm, adding CC.
When Pelakka Wurm dies, its second ability and Nim Deathmantle trigger.
Resolve the Pelakka Wurm trigger, causing you to draw a card.
Resolve the Nim Deathmantle trigger from step 2, causing you to pay 4 to return Pelakka Wurm from your graveyard to the battlefield, and attach Nim Deathmantle to it.
When Pelakka Wurm enters the battlefield, its first ability triggers, causing you to gain 7 life.
Trudge Garden triggers, causing you to pay 2 to create two 4/4 Fungus Beast creature tokens.
Activate Ashnod's Altar twice by sacrificing the Fungus Beasts, adding CCCC.
Repeat.
This loop transforms the natural life-giving properties of Pelakka Wurm into an engine of endless rebirth and recycling. By feeding the Wurm to Ashnod's Altar, you generate the exact mana required to fund Nim Deathmantle's revival trigger, which brings the Wurm straight back to the battlefield. Every single return triggers the Wurm's life-gaining enters-the-battlefield ability, which in turn awakens Trudge Garden; thanks to Doubling Season turning that single trigger into a pair of massive Fungus Beast tokens, sacrificing those tokens back to Ashnod's Altar yields a net surplus of mana to keep the entire machine spinning forever while drawing your entire deck.