Mono-green Landfall relies heavily on landfall triggers from Mossborn Hydra, Icetill Explorer, Sazh's Chocobo, and Earthbender Ascension. Torpor Orb does not stop those, because landfall triggers when a land enters and lands are not creatures. It would also shut off the enter-the-battlefield triggers on our own creatures, so it stays in the sideboard. The ooze gives us a repeatable way to exile cards from graveyards, including Esper Origins, which they can flash back from the graveyard. It also makes a Mutagen token each time, which we can use to grow our creatures. Flashfreeze comes in because their threats are green: Mossborn Hydra, Icetill Explorer, Sazh's Chocobo, Mightform Harmonizer, Earthbender Ascension and Sapling Nursery are all legal targets. The wondrous wasp and spyglass siren are our weakest cards here, and the siren's 1/1 body does little versus Mossborn Hydra, so they come out for cards that interact with their engine.

Mono Green's key threats are green creatures, making Flashfreeze a clean blowout against Mossborn Hydra, Icetill Explorer, and Mightform Harmonizer. Day of Black Sun sweeps their small landfall creatures and mana dorks before they snowball counters. Requiting Hex is cut since it can only hit mana value 2 or less, so it misses Mossborn Hydra, Icetill Explorer, and Mightform Harmonizer. Shoot the Sheriff stays in because it destroys any non-outlaw creature regardless of size, so it still answers a Mossborn Hydra once it has grown. We Say Thee Nay! is weak against a deck that doesn't mind paying a tax to resolve ramp spells early.

Mono Green Landfall relies heavily on landfall triggers (Mossborn Hydra doubling counters, Icetill Explorer milling, Mightform Harmonizer doubling power), and Torpor Orb does nothing about those, since it only stops abilities that trigger when creatures enter. It also shuts off our own Dream Beavers, Floodpits Drowner, and Tidebinder, so it stays in the sideboard. Flashfreeze is excellent since their creatures and key enchantments are all green. Day of Black Sun at X=2 or X=3 wipes their early board of mana dorks and small hydras before they can scale out of control. Spyglass Siren is too small to matter against a deck that wants to go over the top with giant trampling threats, and one Nowhere to Run comes out since -3/-3 barely dents a growing Mossborn Hydra. Bitter Triumph stays in, since it kills a creature of any size.