Gruul Delirium pressures you with Patchwork Beastie and Wildfire Wickerfolk while protecting its threats with Blossoming Defense and pushing through extra damage with Violent Urge and Break Out, so you need a sweeper that survives their pump spells. Slagstorm cleans up their early creatures before they can become problematic, and Broadside Barrage gives you reach to finish the game once the board is stabilized. Spell Pierce is weak against a deck full of creatures rather than reactive spells, so it's cut for more impactful answers. Hold up removal for their key threats like Inti, Seneschal of the Sun since it generates ongoing value if left unanswered.