BRG is a grindy sacrifice/graveyard deck with Fanatical Offering, Rottenmouth Viper, and The Sackville-Bagginses all caring about the graveyard and sacrifice synergies, so Rest in Peace shuts off a huge chunk of their value engine while still letting us cast our own spells. Beza is a great top-end body that stabilizes against their small aggressive creatures and generates card/life advantage. Erode adds another clean answer to their bigger threats like Mutagen Man. We trim card selection and a counterspell mode since this matchup is more about surviving their board and grinding, not protecting our own spells from countermagic they don't run much of.

Izzet Spellementals is red/blue, so Flashfreeze counters their key red spells like Prismari Charm and Burst Lightning while leaving Hearth Elemental (also red, and thus a valid Flashfreeze target) exposed too. Spell Snare is excellent against their two-mana suite: Prismari Charm and Flow State. Disdainful Stroke answers Eddymurk Crab and Sunderflock, their most punishing top-end. We cut our card draw spells since this is a countermagic and tempo mirror-style fight where we need to be proactive with answers rather than drawing extra cards, and Erode is a worse answer than hard counters against a deck that plays around removal with flash creatures.

Mono-Green Landfall is entirely green, making Flashfreeze a great blanket answer to their key spells like Mossborn Hydra, Mightform Harmonizer, and Earthbender Ascension. Negate backs that up against noncreature spells like Glimpse the Core. Erode is efficient removal for their big landfall-fueled threats. We trim card draw spells since this matchup is a race/removal fight rather than a grind, and Seam Rip is weaker here since most of their key permanents cost more than 2 mana.