This loop relies on Yedora, Grave Gardener to continually recycle your fallen creatures into untapped lands, turning every trip to the graveyard into fresh mana potential. When you feed Granite Witness to Thermopod, Yedora's static ability immediately drags it back to the battlefield face-down as a Forest land, which can then tap for green mana to help pay your costs. Skirk Alarmist steps in as the engine's core activator, using its tap ability to flip Granite Witness back face-up; this simultaneously triggers the Witness's own ability to untap Skirk Alarmist so the loop can start anew.