Gruul Ponza plays no blue spells, so Pyroblast is dead, and while Hydroblast can counter red spells like Boarding Party, Envelop is live against their land-destruction sorceries like Mwonvuli Acid-Moss and Thermokarst, protecting our fragile artifact-land manabase from being blown out. Toxin Analysis does little against their ramp-into-big-creatures plan, so trading it for proactive disruption of their land destruction is worthwhile. Keeping our artifact lands online is critical since our whole engine depends on affinity and metalcraft, making Envelop a high-value inclusion here. We still want to race quickly before Annoyed Altisaur or Boarding Party's cascade value takes over the game.