Wall of Mist

Toughness five is the number that does the work here: it walks under most of an aggressive early curve without trading down, denying the beatdown deck the tempo swing it needs while blue spends its real cards reacting. The body will never attack (defender guarantees that) and it makes no value on its own, so the entire contract is survival: stay alive long enough for the controlling deck to find its footing and convert time into card advantage. That is a very old shape. The cheap, fat blue blocker traces back to the earliest walls, the pieces that made the color's "do nothing, then win" plan something the first few turns could actually support before the counterspells and card draw came online. It carries no upside beyond blunting damage, which is why it has recurred as filler across so many printings: a defensive floor for a color that would rather stall than race, priced so low it barely competes with the spells it is protecting.