Esper Stormblade

The white-or-black slot in the cost is the structural cleverness: blue plus either of those colors casts the Stormblade, but because that pip reads as both white and black no matter which mana pays for it, the printed card is multicolored on every axis the rules care about. That matters less for its own anthem (it cannot count itself; the text demands another multicolored permanent) than for what it announces about its intended home, a board where every other permanent is also gold, so a deckbuilding constraint becomes a standing bonus rather than a one-time payoff. Satisfy the condition and you have a 3/2 flier for two; fail it and the body sits at 2/1 on the ground. What keeps it more flexible than a static lord is that the buff lives on this creature and rechecks continuously, at no mana and no decision: trade away your last gold permanent in combat and the Stormblade sheds its flying and a point of stats mid-step; replay one and it climbs back into the air. This is a conditional creature reduced to a single recurring question (is the rest of your board actually multicolored?), paying out the identical answer every turn you can say yes.