Mono-Blue Terror relies on graveyard density to cheat out Tolarian Terror and Cryptic Serpent, and on Counterspell/Dispel/Spell Pierce to protect its plan, so proactive disruption is key. Mesmeric Fiend strips a key threat or counterspell from their hand before they can deploy it, and it dodges their removal-light suite. Faerie Macabre can discard itself to exile cards from their graveyard, directly hurting the cost reduction on Cryptic Serpent and Tolarian Terror, and its flying body can also block Delver of Secrets after it transforms. Nezumi Linkbreaker and Sadistic Glee are too slow and don't interact with the opponent's plan, so they come out for more proactive hand disruption and graveyard hate.