The Story Goes On

Gambit can only be unlocked in the Snow level, and relies on some RNG. You'll need to play an instance of the Snow level where the yin yang symbol is spawned in a room (same as that required for the Snow Page). Use the yin yang symbol room to invert the colors like you did for the Snow Page. With the colors inverted, go room to room until you find a white character running around. Hit him with your sword until you unlock Gambit and this achievement.