Boros Moxite plays a wide array of small creatures (Thraben Inspector, Kor Skyfisher, Glint Hawk, Sneaky Snacker) alongside removal like Journey to Nowhere and Galvanic Blast, so Suffocating Fumes' -1/-1 sweeps away their many 1-toughness bodies and shrinks the rest ahead of an attack. Duress proactively strips a key removal spell like Journey to Nowhere or a combat trick like Rally the Peasants before it can be used against your Crypt Rats or during a critical turn. Keep the bulk of your Fog suite intact since their gameplan still relies on combat damage, trimming only redundant Tangle copies for these additions.