Sky Weaver

Color identity is the entire reason this Metathran exists. The ability grants flying only to white or black creatures, which makes no sense as a build-around in mono-blue and perfect sense in a block built around two-color pairings and gold rewards. It is allied-color scaffolding rendered as a humble blue activator: anchored in blue but pointing outward, it belongs in Azorius or Dimir shells where it can repeatedly lift your partner color's ground-bound bodies over the battle line for two mana a pop. The flavor tracks the mechanics: the Metathran were Urza's engineered soldiers, and a Weaver hoisting allied troops above the line is exactly the supporting role the creature type filled across that era. Strip the restriction and you have a generically useful evasion-granter; with it, you have a card that only does its job when your deck is built the way the design wanted you to build it. That is the discipline at work: the white-or-black clause is not a downside so much as a tax paid in deckbuilding commitment, steering the activator into the specific blue-plus-allied-color shells it was printed to reward rather than letting it float into any blue list as a colorless utility piece. The conditional is the whole point; it converts a flat ability into a statement about which two colors you chose to commit to.