Mono Green Landfall floods the board quickly with Llanowar Elves and Icetill Explorer before threatening to go wide with Mightform Harmonizer and Earthbender Ascension. Bring in Day of Black Sun as a sweeper to reset their board state, and Leatherhead, Swamp Stalker as a large threat that can dominate ground combat while generating value. Cut a pair of narrow, reactive cards that do little to stop their proactive board development. Your priority post-board is to stabilize with removal and Requiting Hex, then deploy your larger threats to take over the mid-game.