This matchup is a grindy colorless-mana midrange fight. Obsidian Charmaw flies over most of their ground creatures, destroys a nonbasic land on entry (Urza's Saga, Eldrazi Temple, Ugin's Labyrinth and Boseiju all qualify), and gets cheaper against their colorless-heavy manabase. Meltdown is a modest sweeper for their cheap artifacts like Springleaf Drum, Blade of the Bloodchief, Haywire Mite, Vexing Bauble, Soul-Guide Lantern and Talisman of Resilience (at X=2), plus the Construct tokens that Urza's Saga makes. It cannot hit Urza's Saga itself, which is an enchantment land, so don't count on it against their land base. Unholy Heat comes in as cheap removal for early creatures like Basking Broodscale, and with delirium it deals enough damage to kill much bigger bodies. Street Wraith and extra cantrips come out since they do little against their bigger bodies and this game goes longer, favoring card quality over speed. Keep Thoughtseize and Orcish Bowmasters in to disrupt their draws; Bowmasters is best against extra draws like the draw from Kozilek's Command.

Izzet Prowess is a fast creature-removal race where Unholy Heat is excellent, cheaply killing Monastery Swiftspear, Dragon's Rage Channeler, and Slickshot Show-Off even before delirium, and for 6 once it's online against anything bigger. Fear of Missing Out comes out since its delirium combat trigger is too slow against a deck trying to kill you with small creatures and burn before that matters. Surgical Extraction can strip a key Expressive Iteration or key removal piece from their graveyard/hand to disrupt their flow, paid for with life rather than mana. Keep Lightning Bolt and Thoughtseize in as premium removal and disruption against their low curve.

Meltdown is a strong answer here: at X=1 it destroys Blade of the Bloodchief along with Urza's Saga Construct tokens and the small colorless artifacts they play, such as Vexing Bauble, Springleaf Drum, Haywire Mite and Soul-Guide Lantern. It doesn't touch Basking Broodscale or Eldrazi Spawn tokens, since those are creatures, so it trims their support rather than stopping the Broodscale loop directly. Unholy Heat comes in as cheap instant-speed removal for creatures like Basking Broodscale (a 2/2) and Glaring Fleshraker (a 2/2), since even its base 2 damage kills them before they grow. Street Wraith comes out since it does nothing to interact with their combo and this matchup is about having interaction ready, not filling the graveyard for delirium. Keep Thoughtseize to strip Blade of the Bloodchief or Basking Broodscale before they assemble the loop, and keep Lightning Bolt to kill Broodscale before it starts adapting. Orcish Bowmasters' 1 damage won't kill a Broodscale on its own, but it can kill an Eldrazi Spawn token.