Mono Green is a landfall-centric ramp deck built around Mossborn Hydra and Mightform Harmonizer, both green creature spells that Flashfreeze can counter outright. Get Lost is excellent removal for their big threats or for enchantments like Earthbender Ascension and Sapling Nursery, since it destroys any creature, enchantment, or planeswalker. Demolition Field is poor here since their deck floods with basic Forests, and trimming a copy of Abandon Attachments and Stock Up for more proactive answers helps since this matchup is about racing their ramp rather than grinding card advantage. Keep Avengers Disassembled in as a sweeper against their small creatures like Llanowar Elves and Sazh's Chocobo, but remember its 3 damage won't kill sturdier bodies like the 2/4 Icetill Explorer.
Dimir Midrange leans on Kaito, Bane of Nightmares and Enduring Curiosity to grind out card advantage, plus Requiting Hex and Bitter Triumph for removal. Negate is strong against Kaito (a noncreature spell) and their removal suite, and Disdainful Stroke catches both Kaito and Enduring Curiosity at mana value 4. Ral, Crackling Wit adds a second proactive threat that generates value every turn you're casting spells. Demolition Field has targets among their many nonbasic lands, but they get a basic land back, so it is mostly a land-for-land trade; it comes out in favor of more relevant interaction. Keep Avengers Disassembled and Thor, God of Thunder: Avengers Disassembled sweeps away Floodpits Drowner and their other small creatures, though it cannot hit Kaito since he is only a creature during his controller's turn, while Thor's trigger can deal damage to Kaito directly whenever you cast a noncreature spell.
BRG is a value-creature midrange deck full of enters-the-battlefield triggers like Biotech Specialist and The Sackville-Bagginses. Torpor Orb shuts off those enters-the-battlefield triggers, severely blunting their value engine, while Get Lost provides unconditional removal for their bigger threats like Smaug the Magnificent or Wolverine, Fierce Fighter. Demolition Field is slow here, since it costs mana and a land of our own just to trade for one of their lands, so it comes out along with one Abandon Attachments for more impactful cards. Avengers Disassembled stays in as a sweeper against their many small creatures.
Suggested new sideboard cards to pick up for the current metagame.
Missing sideboard cards? The full 15-card sideboard runs about $57.53.
Buy sideboard on Manapool