Spy Combo fills the board with small creatures like Overgrown Battlement, Wall of Roots, Saruli Caretaker, and token generators, and Breath Weapon's 2 damage to each non-Dragon creature wipes most of their mana dorks and defenders, setting back their ramp into Dread Return or Troll of Khazad-dum. This slows their combo assembly significantly since they rely on a critical mass of cheap bodies. Annoyed Altisaur and Colossal Dreadmask are the easiest cuts, trading top-end for a cheap sweeper that answers their actual gameplan. Keep your mana ramp and pressure package intact to race them before Dread Return comes online.