Vicious is interesting, a tweak on doublestrike that seems more intuitive. While flavorful on a ninja, the mechanic doesn't feel blue to me though.

I kinda agree that it doesn't feel exactly blue. However, I think blue does needs to have some color shifting for it to have more aggressive, combat oriented style while still remaining true to itself (more tempo, less draw-go). For one thing, I would rather have this in blue than, say, afflict.