Golgari is a grindy midrange deck full of small creatures (Badgermole Cub, Graveyard Trespasser) and removal, so Anger of the Gods and Brotherhood's End punish their early plays, and Brotherhood's End also damages Professor Dellian Fel. Be aware that three damage won't kill Sentinel of the Nameless City (toughness 4) or Sheoldred, the Apocalypse (toughness 5), so time the sweepers for boards built around their smaller creatures. Spell Snare only counters a spell with mana value 2, so it picks off Go for the Throat, Badgermole Cub, and Tear Asunder; it can't hit Fatal Push (mana value 1), and Abrupt Decay can't be countered at all. Change the Equation handles cheap removal like Fatal Push and Go for the Throat or discard like Thoughtseize with its mana value 2 or less mode, and its other mode can counter a green spell such as Professor Dellian Fel. Negate and Fires of Victory come out to make room for these cheaper counters, since Fires of Victory also gets weaker as your hand empties in a grindy game. Keep Indomitable Creativity and Fable in since they generate card advantage and bodies against their removal-heavy plan.

Izzet Cauldron leans on cheap cantrips and counters (Consider, Opt, Sleight of Hand, Stubborn Denial) to power out big creatures like Hearth Elemental, Eddymurk Crab, and Sunderflock. Damage-based sweepers like Anger of the Gods and Brotherhood's End are not worth bringing in here, since all of those creatures have 5 toughness and survive 3 damage. Change the Equation is excellent since its first mode counters cheap spells like Consider, Opt, Sleight of Hand, Fiery Impulse, and Prismari Charm at mana value 2 or less, and its second mode can counter a red spell with mana value 6 or less, such as Hearth Elemental. It cannot counter the blue Eddymurk Crab or Sunderflock, so save it for the cheap spells and Hearth Elemental. Fires of Victory is trimmed since it is awkward to rely on against their cheap spells and counters, and Negate stays in to answer their noncreature spells.

This is the exact mirror, so the game comes down to who answers the opposing Fable tokens and Indomitable Creativity better while protecting your own plans. Mystical Dispute is excellent here since it costs only {U} against the mirror's blue spells like Deduce and Make Disappear. Spell Snare cleanly answers Deduce, Make Disappear, and Negate at mana value 2, while Test of Talents strips their copy of whatever instant/sorcery you counter, which is strong against their singleton Flashback or Three Steps Ahead. Negate and Fires of Victory are cut since Negate overlaps with better options and Fires is mediocre when both sides are trading removal spells of similar efficiency.