Mono Green Landfall ramps with mana dorks and snowballs landfall creatures (Mossborn Hydra, Icetill Explorer, Mightform Harmonizer) that outgrow single-target removal. Split Up is a sorcery, so it only works on our own turn. Cast it precombat and choose the mode that destroys all tapped creatures. Our creatures are untapped then, so they survive, while any of their creatures that attacked or tapped for mana on their turn are still tapped and die. Don't choose the untapped mode, since it would wipe our own board. Burst Lightning is too small against hydras that can snowball past 4 toughness via landfall counters, so two copies come out. We keep one to kill a Llanowar Elves or Sazh's Chocobo early. Doorkeeper Thrull stays in the sideboard: it doesn't stop landfall triggers or Earthbender Ascension, and it would turn off the enters-the-battlefield triggers on our own Hellkites and Sarkhan. Keep the full aggressive core since we still want to race before their mana advantage takes over.

Dimir Midrange relies heavily on recursive and graveyard-fueled value: Enduring Curiosity returns itself from the graveyard, Kaito ninjutsus back, and they grind with card draw engines. Rest in Peace shuts off Enduring Curiosity's return trigger and any flashback/escape-style recursion while we race with our aggressive creatures. Burst Lightning is undersized against their 3/4 and 4/3+ bodies like Kaito and Spyglass Siren's backup threats, so we trim it for the graveyard hate. Keep the full creature suite since we need to close the game before their card advantage engines take over.

BRG goes wide with cheap creatures like Gene Pollinator, Greedy Freebooter, and Rottenmouth Viper fodder, making Split Up a strong sweeper against their board-flooding plan. Because it's a sorcery, we cast it on our own turn, before attacking, choosing to destroy all tapped creatures. Their creatures that attacked or tapped for mana (like Gene Pollinator) stay tapped through our turn, while our own untapped creatures survive. Burst Lightning kills their small creatures one at a time but can't answer a big threat like Rottenmouth Viper, so we trim a couple copies. This is a racing matchup where our fliers (Momo, Nova Hellkite, Smaug) go over the top of their mostly ground-based value creatures, so we keep the core aggressive plan intact.