Mono Green Landfall's early creatures (Llanowar Elves, Sazh's Chocobo, Icetill Explorer) are all mana value 4 or less, making Day of Black Sun at X=4 a genuine sweeper here, destroying their Sazh's Chocobo, Llanowar Elves, Icetill Explorer, and Mossborn Hydra while leaving our own bigger threats like Overlord of the Balemurk and Uldaros Theorix untouched. Flashfreeze is excellent since every opposing spell is green, countering their Mossborn Hydra, Esper Origins, or Earthbender Ascension outright. Duress is weak here since they have very few noncreature spells worth discarding, and Winternight Stories is too slow against their land-ramp aggression, so both come out.