Gruul Ponza has no blue spells, so Red Elemental Blast and Pyroblast stay in the sideboard, and their threats like Annoyed Altisaur and Bramble Wurm are too high-toughness for Cast into the Fire's small damage mode to matter much. End the Festivities can pick off their 0/1 Eldrazi Spawn tokens and chip a point of damage off their face, marginally helping the race. This matchup is mostly about outracing their land destruction plan (Thermokarst, Mwonvuli Acid-Moss) before they stabilize with big green threats, so keep the core engine intact and prioritize fast starts over interaction.