Claustrophobia

Pauper is where Claustrophobia earns its slot — blue has limited hard removal at common, and a permanent tap effect on a threat is often good enough to win the game. In Commander, it's too slow and too vulnerable: one Disenchant, one bounce spell, or one flicker effect undoes the whole thing, and three mana for conditional removal doesn't scale to a four-player table. Legacy, Vintage, and Modern all have access to removal so far above this rate that Claustrophobia is essentially unplayable in competitive contexts. Pioneer is the same story — if you're in blue and need a creature answered, better options exist at every point on the curve.