Serra Avenger

The restriction is the whole rate. A 3/3 flier with vigilance for two white mana is a statline that should not exist this cheap, so the card pays for it with time: it sits dead in the opening hand through the first three turns, then comes online the moment the embargo lifts. That sequencing inversion is the clever part. Most aggressive white creatures want to be cast as early as possible; this one is barred from the precise window most beaters are at their best, and arrives at full value in the midgame turns when a vanilla two-drop would already be outclassed. The design trades the curve's front end for an absurd back-end rate, betting that a deck built around it spends its first three turns elsewhere and reaches turn four wanting a threat that blocks, races, and overperforms its cost. It rewards a real second curve rather than a pile of one-cost spells, since a hand that idles until turn four is exactly the hand this card was not built for. The vigilance turns it from a clock into wall-and-clock at once, applying pressure while still answering a flier across the table. It dies to the cheap removal that kills everything (a 3/3 is still inside Lightning Bolt range), but the trade you offer is a two-mana spell for their one-mana answer, deferred several turns to a point where the tempo math has shifted in your favor.