Mono Green Landfall ramps hard with Llanowar Elves and fetches like Fabled Passage, so Sunspine Lynx can punish their nonbasic lands (Escape Tunnel, Fabled Passage and Ba Sing Se) while they are on the battlefield, and it shuts off their lifegain entirely. Escape Tunnel and Fabled Passage are sacrificed to fetch basic lands, so they stop counting once they are used, and the basics they fetch don't add to the damage. Note that the Lynx also deals damage to us based on our own nonbasic lands. The Legend of Roku provides card advantage and an eventual firebending threat. Valley Flamecaller's damage amplification matters less here since we're not racing as aggressively against their ramp plan, and Stinging Vitriol's 2 damage is too slow against a deck not relying on precise life totals. Prioritize racing before Mightform Harmonizer and Earthbender Ascension take over the board.