Thorns + bucc with no stun mastery = bossing bucc?

What if critical doesn't work the way you think? What if it depends on the class itself? Even though a Viper may not have Stun Mastery at all, Thorns may not have an effect, since it would look for the class or the class' ability to cause critical without Thorns itself. Even tough there's 0 points, it would still look for stunned monsters before the critical would activate.