Mystic Forge Combo is an artifact-based engine deck (Grim Monolith, Mystic Forge, The One Ring, Urza's Saga) that runs very few creatures, so Cabal Therapy's flashback-by-sacrificing-a-creature is awkward and its discard mode is often guessing against a hand full of artifacts and lands. Collective Brutality's discard mode can only take an instant or sorcery, so it can't hit artifacts like The One Ring or planeswalkers like Karn, the Great Creator, but it can strip Kozilek's Command or Eldrazi Confluence. Its -2/-2 mode also kills a Glaring Fleshraker if they deploy one, and the drain mode gives some extra value. Keep Thoughtseize and Unmask at full count since they can take their artifact and planeswalker engine pieces before those resolve, which is the best way to prevent their engine from ever coming online. This matchup is a race to assemble our reanimation plan before their engine takes over, so prioritize disruption over removal.