This matchup is a race against Eldrazi ramp and big colorless threats, not a counterspell war. Stubborn Denial and Spell Pierce come out because they only hit noncreature spells and can't touch Emrakul, Sowing Mycospawn, or Devourer of Destiny, which are creature spells. Obsidian Charmaw comes in as a flying beater that is often discounted by their colorless-producing lands, and its enter trigger destroys a nonbasic land such as Eldrazi Temple, Ugin's Labyrinth, or Urza's Saga, slowing their ramp. Rest in Peace exiles cards that would hit their graveyard, which keeps Emrakul, the Promised End expensive (its cost reduction counts card types in their graveyard), turns off Shifting Woodland's delirium ability, and exiles the cards Malevolent Rumble would put into the graveyard. Keep Leyline Binding in as your primary answer to their bombs, since it exiles any nonland permanent and Emrakul's protection from instants doesn't stop it. Keep Lightning Bolt in to kill early creatures like Basking Broodscale and Sowing Mycospawn, but don't expect it to handle Emrakul or Devourer of Destiny.

The combo wants to resolve Basking Broodscale with Blade of the Bloodchief equipped, so Wear // Tear's artifact half, Wear, is a clean two-mana answer to Blade before the loop starts. Obsidian Charmaw destroys Urza's Saga or Eldrazi Temple, cutting off the lands that tutor for and power their combo pieces, while also presenting a fast flying clock. Containment Priest exiles any nontoken creature that enters the battlefield without being cast, which only matters if they find a way to put creatures into play that way, but it still gives us a flash 2/2 body. Stubborn Denial and Spell Pierce are cut since they can't counter creature spells like Basking Broodscale, and countering noncreature spells does nothing against abilities already on the battlefield, such as Basking Broodscale's adapt (an activated ability) or Blade's 'whenever a creature dies' trigger (a triggered ability). Quantum Riddler is too slow against a deck that can win out of nowhere.

Izzet Prowess wants to go wide with cheap spells and small creatures, so Consign to Memory is excellent against their colorless cantrips and triggered abilities like Cori-Steel Cutter's Flurry token creation. Stern Scolding comes in to cleanly counter Monastery Swiftspear, Dragon's Rage Channeler, or Slickshot Show-Off for a single blue mana. Quantum Riddler is too slow and clunky against a deck this fast, so it comes out entirely. Stubborn Denial is weaker here since our own creatures rarely hit power 4 early enough to make it a hard counter against their cheap removal-light plan, so two copies are cut in favor of more proactive answers.