Weapon "W" is an achievement in the Blood and Wine expansion and requires one to develop a mutation.
While playing, typically right after the main quest Blood Run, you'll soon run into a messenger in Beauclair who gives you a letter that'll give the secondary quest Turn and Face the Strange. Complete this quest to the end to unlock the special mutation character panel. The cheapest one requires 2 ability points and 2 greater mutagens of the same color (red, green, or blue). Unlock one and you'll get the achievement.
Trivia[]
- The name of the achievement is a reference to Marvel Comics' Weapon X, a secret genetic research project that tested subjects with superhumans abilities and enhanced them through crude experiments.