Azorius Keyrune

The Azorius entry in the guildmage-era manarock cycle, where each guild got a three-mana artifact that fixed its two colors and, for a guild-colored payment, animated into a creature whose stats and keywords matched the guild's identity. White-blue drew the body best suited to the way that pairing wins: a 2/2 flier, the kind of evasive clock most useful in a deck that grinds the board to a stall behind counterspells and removal. The until-end-of-turn clause is the restriction that earns the rest. The card is always an artifact, so it never escapes artifact removal, but as long as you leave it inert it offers nothing for creature removal to bite; it sits on the board as fixing, not as a target, until the turn you choose to spend mana animating it. That choice is the whole appeal: you swing the Bird in only after a sweeper has passed or when a flier closes the game, and you never have to leave a vulnerable body exposed in between. It is mana fixing that refuses to be a dead draw in topdeck mode, the activation tucked away as a late-game option rather than a liability, which is exactly the niche a two-color control deck most wants filled.