Spy Combo is a green/black ramp-into-big-creatures deck with no red, blue, or artifact permanents worth targeting with our sideboard tools (Pyroblast/Red Elemental Blast need blue, Smash to Smithereens needs a relevant artifact, Searing Blaze wants a creature plus landfall which is awkward against their mana dorks already in play). Relic of Progenitus could theoretically hit their graveyard-based Dread Return or Troll of Khazad-dum recursion, but their deck doesn't heavily rely on graveyard recursion as a core engine, making it a low-impact inclusion that costs us tempo in a race we should be winning on raw speed. Our best plan is simply to goldfish as fast as possible with the unmodified core burn plan, since Spy Combo's early turns are spent ramping and filtering rather than interacting with our board or life total. No sideboard changes are needed; keep the full 75 as configured.