Izzet Delver is entirely blue and red, and Pyroblast hits the blue half of it. It counters their blue spells like Brainstorm, Ponder, Flow State, Daze, or Force of Will, or outright destroys a blue Murktide Regent. Their red cards, such as Lightning Bolt and Dragon's Rage Channeler, are not legal targets for Pyroblast. We cut our own Murktide Regent since both decks leaning on delve and their graveyards leads to an awkward race we don't need to engage in given our better removal suite. Extra Consign to Memory is mostly about triggered abilities: it can counter things like Dragon's Rage Channeler's surveil trigger or a Cori-Steel Cutter flurry trigger, and it can counter their colorless Mishra's Bauble while it is a spell on the stack. It can't counter their blue or red spells such as Murktide Regent or Cori-Steel Cutter, since those aren't colorless. Prismatic Ending comes out since converge makes it hard to reach higher mana values and our other removal is better in this matchup.