Riverfall Mimic

Cast a single spell that registers as both blue and red, and the body wakes up: a 3/3 that walks past the whole board for the turn. That is the entire pitch, and it rests on one of the narrowest inputs the game has ever asked a creature to count. The trigger demands a spell that is simultaneously blue and red, so the Shapeshifter has only two settings: a vanilla 2/1 in any deck that ignores the requirement, or a recurring evasive threat in one engineered to satisfy it. There is no dial between. This sits among a cluster of two-color creatures from the same design moment, each of which paid off the act of casting a gold spell of a specific guild rather than caring what that spell did. The casting itself is the reward, which is an unusual axis: most creatures reward you for what you play, not for how its colors happen to combine. The clause is a one-time flip per turn; it sets base power and toughness to 3/3 and grants unblockable, so a second qualifying cast that turn adds nothing the first did not already deliver. The flexibility lives entirely in deckbuilding, in whether you can reliably produce that blue-and-red spell, not in stacking triggers within a single turn. The body is forgettable on its own; the cast-condition it implies, and the kind of deck willing to meet it, is where the design actually lives.